fix(templates): curate the agent template catalog — hide fixtures, order starters first (#1513)

[vybe]

Summary

• GET /api/templates no longer surfaces internal test/canary fixtures, demo agents, or the auto-deployed trinity-system agent as real user templates — they're excluded via an explicit hidden: true template.yaml flag (not fragile name-matching), while staying creatable-by-id so the canary/test harness is untouched.
• Real starters now lead: both template builders surface a coerced-int priority, so the router's (priority, display_name) sort orders scout/sage/scribe (priority 20) ahead of the dd-* suite.
• The Templates tab and Create Agent modal now show the same curated set (Templates.vue was GitHub-only).

Acceptance criteria (all met)

• Fixtures excluded via an explicit signal (hidden: true), not name matching
• Broken config/agent-templates/cornelius/ stub removed
• Ordering surfaces real starters first; no fixture outranks a genuine starter
• Templates tab + CreateAgentModal show the same curated source
• A test asserts fixtures are excluded (+ a convention guard so they can't silently reappear)

Changes

• src/backend/services/template_service.py — _coerce_priority() helper; surface priority+hidden in _build_local_template, priority in _build_template; filter hidden in get_local_templates() (LIST only — single-id + creation-by-id preserved).
• config/agent-templates/*/template.yaml — hidden: true on the 7 test/canary fixtures, 2 demo agents, and trinity-system.
• config/agent-templates/scribe/template.yaml — quote the usage: value (an unquoted format: colon made the file invalid YAML, so this core starter was silently dropped from the catalog).
• src/frontend/src/views/Templates.vue — add a Starter (local) Templates section.
• config/agent-templates/README.md + docs/memory/feature-flows/template-processing.md — reconcile docs with the hidden set and document the flag.
• tests/unit/test_local_templates_listing.py — exclusion, single-id survival, priority coercion, router-sort regression, real-catalog convention guard.

Notable finds during review

• Recovered a missing starter: scribe was already absent from the catalog because its template.yaml failed to parse — fixed.
• Prevented a latent 500: surfacing a raw priority: null/"high" would TypeError the router sort; _coerce_priority guards it (with a regression test).
• cornelius/ carried no git-tracked files (its only contents are globally gitignored .trinity/ hooks) and never appeared in the catalog (no template.yaml) — removed the local artifact; produces no diff.

Test plan

• pytest tests/unit/test_local_templates_listing.py — 19 passed (11 existing + 8 new)
• Adjacent template tests unaffected — test_data_paths_template_surface, test_deploy_writable_templates (5), test_templates (5 passed / 3 skipped)
• End-to-end catalog simulation against the real config/agent-templates/: fixtures excluded, scout/sage/scribe present and ahead of dd-*, hidden fixtures still resolve by id
• Manual: Templates tab + Create Agent modal render the same curated set

Follow-up (deferred, out of scope)

• Extract a shared <TemplateCard> component — the new local card markup mirrors the GitHub card; deferred to avoid pulling CreateAgentModal into a P1 bug fix.

Fixes #1513

🤖 Generated with Claude Code

[dolho]

Review: ✅ Approve

Clean fix for #1513. Highlights:

• hidden: true over name-matching — machine-enforced exclusion, surfaced (not filtered) in _build_local_template so single-id resolve + creation-by-id still work for the canary/test harness; only get_local_templates() (LIST) excludes. Right seam.
• _coerce_priority prevents a real latent 500: a present-but-null/string priority: would TypeError the router's (priority, display_name) sort. Bool-exclusion (isinstance(True, int)) is a nice touch. Regression-tested.
• Recovered scribe — the unquoted usage: colon made the YAML invalid, silently dropping a core starter. Good catch.
• Real-catalog convention guard fails CI if a future fixture forgets the flag.

Verified the live template dir is repo-root config/agent-templates/ (template_service._local_templates_dir, line 183), so the flagged set is the one users actually see.

Interaction with #1515: cornelius is added there without hidden (intended — flagship), and lands in the default-priority group. Land this PR first so the coercion guard is in place before cornelius's template.yaml is surfaced.