codedb_remote: allow wiki read/actions

[justrach]

Summary

• Allow codedb_remote backend=wiki action=read now that the wiki router exposes /read.
• Add actions to the codedb_remote schema and backend allowlists for both codegraff and wiki.
• Keep the error help text aligned with the advertised action surface.

Validation

• zig build
• Manual MCP JSON-RPC smoke with codedb_remote against api.wiki.codes:
  • action=actions
  • action=read path=README.md lines=1-2
  • paginated action=tree prefix=src/ limit=2 offset=1
  • traversal denial returns HTTP 400 detail

[github-actions]

Benchmark Regression Report

Thresholds: 10.00% and 50,000 ns absolute delta

NOISE means the percentage threshold was exceeded, but the absolute delta was too small to fail CI.

Tool	Base (ns)	Head (ns)	Delta	Abs Delta (ns)	Status
codedb_bundle	480612	494254	+2.84%	+13642	OK
codedb_changes	56205	55159	-1.86%	-1046	OK
codedb_deps	9206	11071	+20.26%	+1865	NOISE
codedb_edit	5839	6025	+3.19%	+186	OK
codedb_find	63102	61044	-3.26%	-2058	OK
codedb_hot	97426	99702	+2.34%	+2276	OK
codedb_outline	264708	257909	-2.57%	-6799	OK
codedb_read	89587	87612	-2.20%	-1975	OK
codedb_search	173880	170472	-1.96%	-3408	OK
codedb_snapshot	256407	256200	-0.08%	-207	OK
codedb_status	215245	215453	+0.10%	+208	OK
codedb_symbol	57473	58812	+2.33%	+1339	OK
codedb_tree	45947	42562	-7.37%	-3385	OK
codedb_word	67726	67425	-0.44%	-301	OK