grammar: accept original SiSU bespoke @key: header dialectHEADmain

Until now the grammar handled only the sisudoc-spine YAML header form.
Real SiSU markup uses two textually disjoint header dialects with an
identical body grammar:

  bespoke (original SiSU, ruby):    yaml (sisudoc-spine):
    % SiSU 4.0.0                      # SiSU 8.0
    @title: Alice's Adventures        title: "Alice's Adventures"
    @creator:                         creator:
     :author: Carroll, Lewis            author: "Carroll, Lewis"

Add bespoke-dialect rules alongside the existing yaml ones; the body
grammar is shared between the two.

grammar.js:
- version_comment widened from /# SiSU(spine)? <ver>/ to
  /[#%] SiSU[^\n]*\n/. Real banners observed across both corpora
  include "# SiSU 8.0", "# SiSUspine 8.0", "# SiSU master 8.0",
  "# SiSU: http://...", "% SiSU 4.0.0", "% SiSU 0.72",
  "% SiSU http://...", "% SiSU markup for 0.16 and later".
- Added sisu_header_field / sisu_header_key / sisu_header_value /
  sisu_header_continuation.
- sisu_header_key whitelists the 14 @keys observed in the sisu
  corpus (including the @links:+ additive variant), parallel to
  the existing yaml header_key whitelist.
- sisu_header_continuation accepts any 1+ space indented line whose
  first non-space character is not a newline. Covers " :sub: val",
  " { text }url" freeform under @links:, and 3+ space wrap-line
  continuations (10690 occurrences across the sisu corpus, almost
  all inside @classify: :topic_register: entries).
- Wired sisu_header_field into _toplevel alongside header_field.

queries/highlights.scm:
- Added @keyword / @string captures for the new sisu_* nodes,
  parallel to the existing yaml header captures.

test/corpus/headers_sisu.txt:
- 12 new cases: % SiSU banner variants, @title: with inline value,
  @creator: + :author:, @date: with multiple sub-keys, @make:
  mixed sub-keys, @links: with freeform { text }url continuations,
  @links:+ additive, full bespoke header block, and a coexistence
  case confirming yaml + bespoke at the same top level.

README.md and sisu-markup_tree-sitter.md:
- Describe dual-dialect support; add sisu corpus results table.

Test results:
- tree-sitter test: 79 / 79 pass.
- sisu-markup-samples/data/samples/ (full sisu corpus): 44 / 65
  parse cleanly (was 0 / 65). current/ layout parses at 20 / 21
  (95 %); the dominant failure mode is the wrapped/ layout
  (7 / 21) which trips the pre-existing one-line-per-paragraph
  limitation, not the new header rules.
- sisudoc-spine-samples/markup/ (full spine corpus): 37 / 46
  unchanged. No regression in the yaml dialect.

Mixing the two dialects inside one document remains parseable but
non-idiomatic; enforcement is left to a future linter pass rather
than the grammar.

(assisted by Claude-Code)

1 files changed, 201 insertions, 0 deletions

diff --git a/test/corpus/headers_sisu.txt b/test/corpus/headers_sisu.txt
new file mode 100644
index 0000000..21f8358
--- /dev/null
+++ b/test/corpus/headers_sisu.txt
@@ -0,0 +1,201 @@
+==================
+SiSU bespoke banner (version)
+==================
+
+% SiSU 4.0.0
+
+---
+
+(document
+  (version_comment))
+
+==================
+SiSU bespoke banner (older version)
+==================
+
+% SiSU 0.72
+
+---
+
+(document
+  (version_comment))
+
+==================
+SiSU bespoke banner (URL form)
+==================
+
+% SiSU http://www.jus.uio.no/sisu
+
+---
+
+(document
+  (version_comment))
+
+==================
+SiSU bespoke banner (freeform note)
+==================
+
+% SiSU markup for 0.16 and later
+
+---
+
+(document
+  (version_comment))
+
+==================
+Bespoke @title with inline value
+==================
+
+@title: Alice's Adventures in Wonderland
+
+---
+
+(document
+  (sisu_header_field
+    key: (sisu_header_key)
+    value: (sisu_header_value)))
+
+==================
+Bespoke @creator with :author sub-key
+==================
+
+@creator:
+ :author: Carroll, Lewis
+
+---
+
+(document
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation)))
+
+==================
+Bespoke @date with multiple sub-keys
+==================
+
+@date:
+ :published: 1865
+ :created: 1865
+ :available: 1865
+ :added_to_site: 2004-04-12
+
+---
+
+(document
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation)
+    (sisu_header_continuation)
+    (sisu_header_continuation)
+    (sisu_header_continuation)))
+
+==================
+Bespoke @make with mixed sub-keys
+==================
+
+@make:
+ :headings: none; none; none; CHAPTER;
+ :breaks: new=3; break=4
+
+---
+
+(document
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation)
+    (sisu_header_continuation)))
+
+==================
+Bespoke @links with freeform link continuations
+==================
+
+@links:
+ { Alice in Wonderland @ Wikipedia }http://en.wikipedia.org/wiki/Alice%27s_Adventures_in_Wonderland
+ { Lewis Carroll @ Wikipedia }http://en.wikipedia.org/wiki/Lewis_Carroll
+
+---
+
+(document
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation)
+    (sisu_header_continuation)))
+
+==================
+Bespoke @links:+ additive variant
+==================
+
+@links:+
+ { ftp archive }ftp://example.org/pub
+
+---
+
+(document
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation)))
+
+==================
+Full bespoke header block
+==================
+
+% SiSU 4.0.0
+
+@title: Alice's Adventures in Wonderland
+
+@creator:
+ :author: Carroll, Lewis
+
+@date:
+ :published: 1865
+
+@rights:
+ :copyright: Lewis Carroll
+ :license: Public Domain
+
+@classify:
+ :topic_register: SiSU markup sample:book:novel;
+   book:novel:fiction:fantasy|children's fiction
+
+---
+
+(document
+  (version_comment)
+  (sisu_header_field
+    key: (sisu_header_key)
+    value: (sisu_header_value))
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation))
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation))
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation)
+    (sisu_header_continuation))
+  (sisu_header_field
+    key: (sisu_header_key)
+    (sisu_header_continuation)
+    (sisu_header_continuation)))
+
+==================
+YAML and bespoke key disjoint at top level
+==================
+
+# SiSU 8.0
+
+title: "Spine document"
+
+@title: Sisu document
+
+---
+
+(document
+  (version_comment)
+  (header_field
+    key: (header_key)
+    value: (header_value))
+  (sisu_header_field
+    key: (sisu_header_key)
+    value: (sisu_header_value)))