Add hooks: vibestretch (resubmission of #5780)

[Eliasjunit]

Resubmission of #5780 with the three fixes from the review, applied verbatim:

• safetyNotes: reworded per suggestion — the optional /vibestretch:statusline skill does edit ~/.claude configuration (explicit user request only, with backup); the hook itself writes only to its own state directory.
• privacyNotes: reworded per suggestion — the script reads the first 4 KB of the hook payload to extract session_id; nothing from prompts or tool output is retained or transmitted.
• scriptLanguage: bash -> sh (the shebang is #!/bin/sh).

Everything else, including the byte-identical scriptBody and copySnippet, is unchanged from #5780. Thanks for the thorough review.

[Eliasjunit]

Closing as a duplicate of #5793 — two of my own windows opened the same resubmission 40 seconds apart. Apologies for the noise.

#5793 is the one worth your time: its scriptBody is byte-identical to scripts/vibestretch.sh at v0.7.1 (288 lines), while this PR carries the pre-0.7.1 body (285 lines) and would fail the same provenance check you ran on #5780. Both otherwise contain your corrected safetyNotes/privacyNotes wording verbatim.