refactor: one declaration renderer, one member partial, one vocabulary

[auscaster]

Core structure work behind #130 and #131, with a regression guard built first.

The guard

test/snapshots/ holds the full rendered Markdown for all 11 fixtures plus the search entries generate() returns and run() never writes to disk. The other suites assert on chosen lines, so anything outside them landed silently. I proved it fails on a one-word label change before relying on it, and every commit below was judged against it.

One declaration renderer

member.proto was 116 lines of parser code duplicating the signature helper, feeding one search-snippet fallback, kept "for classic templates" — a directory the docs tell users to pass and which is not in this repo. compound.proto was written and never read. Both gone; src/signature.ts is now the only thing that knows what a declaration looks like. Net 207 lines deleted.

One visible effect: the macro search snippet was \define ``GGROUP_DEFINE`, now #define GGROUP_DEFINE 1`.

Function pointers (fixes #131)

Parameters came from a hardcoded list of member kinds. Doxygen reports a function pointer as a variable with no <param> elements at all, describing its arguments only in a <parameterlist>, so they fell through and nothing rendered. Parameters now come from whatever evidence exists. And since Doxygen splits int (*retry)(int n) into type, name and argsstring, joining those three restores the declaration without parsing C.

One member partial

The six member sections were near-copies. Measured: 92 lines (cpp/class), 60, 50, and only cpp/class carried source links and relation lists — java/class did not, which settled whether the divergence was design or drift.

They now share one partial per language. Namespace, group and index pages gain the source links and separators; enum tables sit in the same position everywhere. Full blast radius across the corpus: 12 Defined in lines, 13 separators, and the enum table moving.

Member types link (#130)

A member's own section now echoes its type as a link, so a struct member pointing at another type can be followed. Only where the type points somewhere, and only for members that are not callable, since functions already link their types in the parameter and summary tables.

The all-members table now appears only where members are actually inherited. MountainBike keeps it and shows PedalHarder inherited from Bicycle; Bicycle and the ten fixture classes with no bases lose a table that repeated the one below it with less in it.

One vocabulary

SECTION_LABELS, searchCategoryForKind and the return-column set lived in three modules with define → Macros written twice. Now co-located in src/vocabulary.ts. They do not collapse into one table, since kind and section are different axes, so this is adjacency rather than unification.

Bundles the 2.1.17 bump.