chore(release): bump version to 0.5.17

[its-saffron]

Version bump for release v0.5.17. The release will be published after this PR passes the required checks and merges.

dispatch 0.5.17

Fixes

Groomer output is now fully grammar-enforced. The json_schema sent to the
LLM was looser than the output validator, so a small model could emit output the
validator then rejected (seen in prod on the 4B: invented labels like
type/refactor, and an empty proposedTitle instead of omitting it). Label
arrays are now enum-constrained to the allowlist and proposedTitle/proposedBody
carry their length bounds in the grammar itself. (#542)

Image binds all interfaces (HOSTNAME=0.0.0.0). Next standalone binds to
$HOSTNAME, which Kubernetes sets to the pod name — so the server only listened
on the pod IP and the in-app scheduler's loopback POSTs to 127.0.0.1:3000
failed with ECONNREFUSED. Baked into the image; deployments no longer need a
HOSTNAME env override. (#541)

Tests & CI

• github.ts coverage backfill: issue/PR/label helpers, review-decision
  derivation, check-failure filtering, PR-health state mapping (+32 tests,
  closes the last half of test: backfill agent-queue-fetch and github.ts coverage #511). (test(github): backfill coverage for issue/PR/label helpers (#511) #539)
• PR image builds no longer export the buildx cache (~270s saved on every
  release-bump/Renovate PR build). (ci(image): stop exporting build cache from PR builds #540)