hotfix: wiki raw URL has spurious branch segment causing 404

[liplus-lin-lay]

observation

Live cron observation for github-rag-mcp wiki ingestion (after #131 hotfix deploy):

```
Liplus-Project/github-rag-mcp wiki: 6 pages, 0 embedded, 0 unchanged, 6 failed, 0 deleted
No content fetched for Liplus-Project/github-rag-mcp/wiki/installation.ja (all extensions 404)
fetchWikiContent probe md failed for Liplus-Project/liplus-language/e.-...
fetchWikiContent probe markdown failed for Liplus-Project/liplus-language/e.-...
```

#131 fixed the subrequest exhaustion. The remaining failures are pure 404s on every page.

root cause

GitHub Wiki raw URL pattern does not take a branch segment.

```
raw.githubusercontent.com/wiki/{repo}/master/{file}.md -> 404
raw.githubusercontent.com/wiki/{repo}/main/{file}.md -> 404
raw.githubusercontent.com/wiki/{repo}/{file}.md -> 200
```

W4 (#128 / PR #129) implementation hardcoded `/master/` in the URL on the (incorrect) assumption that wiki git repos use master branch. The wiki repos do use master internally (`git ls-remote` confirms), but raw.githubusercontent.com routes wiki content WITHOUT branch in the path.

fix

Remove `/master/` from URL string in two locations:

• `src/poller.ts` `fetchWikiContent` (cron-side ingestion)
• `src/mcp.ts` `inlineDocContent` (search-time include_content for wiki rows)

version

patch (v0.8.5 milestone) — same hotfix milestone as #131.

related

• feat: index GitHub Wiki content into RAG (W4) #128 / PR feat: index GitHub Wiki content into RAG (W4, patch) #129 (W4 wiki indexing implementation, introduced the bug)
• hotfix: wiki ingestion exhausts Worker subrequest budget on initial bulk poll #130 / PR hotfix(poller): cap wiki ingestion subrequest fan-out (#130, patch) #131 (subrequest cap hotfix, unmasked this 404 bug by surviving long enough to reach raw fetch)