feat(ci): add GitLab issue templates and label-automation triage job

[joshjhall]

Summary

• Add GitLab issue templates (Bug Report, Feature Request, Refactor) that
  mirror the H2 body anchors from docs/development/filing-issues.md, apply a
  type/* label via a /label quick action, and embed a machine-readable
  Triage block (- Severity: / - Effort:).
• Add a gitlab-triage policy (.gitlab/triage/triage-policies.yml) that parses
  the Triage block into severity/* / effort/* labels (idempotent via
  forbidden_labels), flags issues missing either label with needs-triage
  plus a note, and clears the flag once fully labeled.
• Add a reusable, schedule-gated CI include (.gitlab/ci/triage.yml) that runs
  the policy with a pinned gitlab-triage version.
• Document the GitLab web-UI filing path in docs/development/filing-issues.md.
• Fix the typos pre-push hook (lefthook.yml) to pass files via
  xargs -d '\n' so the spaced template filenames are not word-split.

This is the GitLab counterpart to the GitHub issue-template work (split from
#228, superseded by #294). It covers the human web-UI filer path; /file-issue
covers the agent path. Both apply the identical taxonomy.

Test plan

• tests/unit/gitlab-templates.sh — 11 structural assertions (templates,
  quick actions, shared + type-specific H2 anchors, valid Triage defaults, YAML
  validity, full label coverage, both needs-triage rules, schedule gate).
• Full unit suite green: 3154 passed / 0 failed.
• yq validates both YAML files; shfmt -i 4 -ci + shellcheck clean on the
  test; typos now passes on the spaced filenames.

Review findings

Pre-PR adversarial review ran (6 of 7 dimensions completed; the 7th agent hung
on a harness stall and was excluded). The one blocking finding — unpinned
gitlab-triage gem executing with an API token — is fixed in this PR (gem
version pinned via GITLAB_TRIAGE_VERSION). Additional high-certainty findings
fixed here: the needs-triage logic now fires when either label is missing
(was: only when both absent), the stibbons labels sync suggestion for
needs-triage was corrected (that label is not skill-owned), the label color no
longer collides with severity/medium, and tests were added for the auto-clear
rule, type-specific anchors, and Triage-default validity.

Deferred as follow-ups:

• Harden GitLab triage CI job (reproducibility + secret handling) #716 — harden the triage CI job (transitive gem deps, image pinning, gem
  cache, token-in-argv, allow_failure alerting).
• Functionally test gitlab-triage regex conditions against template Triage blocks #717 — functionally test the gitlab-triage regex conditions against template
  Triage blocks.

Closes #298