docs: pin source links to full commit hashes

[dobby-coder]

Closes #57.

Three source links in docs/repos/ violated the full-40-char-commit-hash convention:

• docs/repos/cryptify.md:89 — repointed from /blob/main/src/main.rs to commit 2a6dac195ef4efae8758084aaacab04bc9c94206 (latest commit touching that file).
• docs/repos/pg-sveltekit.md:124 — expanded short hash 2b29c1ba18 to the full SHA 2b29c1ba18be39d89380a9dd8dd4d3370e17e0b2. Snippet content unchanged; verified against source.
• docs/repos/pg-sveltekit.md:159 — same hash expansion. While verifying, the in-doc handleSend snippet was missing two lines that exist at +page.svelte L36-L65 (errorMessage = ''; reset and a console.error(...) call). Added them so the snippet faithfully matches the pinned range.

Verification

• curl -sI returns 200 for all three pinned URLs.
• Fetched +page.server.ts and +page.svelte at the full SHA — content matches the docs snippets line-for-line after the small +page.svelte correction.
• Stayed at the pre-consolidation hash for the pg-sveltekit examples per repo memory: snippets cannot simply be repinned across the d6c7f01 consolidation because the API form changed (encryptAndSend wrapper era vs. current pg.open({uuid}).decrypt(...)). A full rewrite against the current API is a separate, larger piece of work.

Reviewer quickstart

```
git fetch origin && git checkout dobby/pin-source-link-hashes && npm install && npm run docs:build
```
Local build succeeded in 24s.