feat: test failure ownership triage — see something say something

Adds two new preamble sections to all gstack skills:
- Repo Ownership Mode: explains solo vs collaborative behavior
- See Something, Say Something: proactive issue flagging principle

Adds {{TEST_FAILURE_TRIAGE}} template variable (opt-in, used by /ship):
- Classifies test failures as in-branch vs pre-existing
- Solo mode defaults to "investigate and fix now"
- Collaborative mode offers "blame + assign GitHub issue" option
- Also offers P0 TODO and skip options

/ship Step 3 now triages test failures instead of hard-stopping on all
failures. In-branch failures still block shipping. Pre-existing failures
get user-directed triage based on repo mode.

Adds P2 TODO for gstack notes system (deferred lightweight reminder).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ship/SKILL.md.tmpl

@@ -26,7 +26,7 @@ You are running the `/ship` workflow. This is a **non-interactive, fully automat
 **Only stop for:**
 - On the base branch (abort)
 - Merge conflicts that can't be auto-resolved (stop, show conflicts)
-- Test failures (stop, show failures)
+- In-branch test failures (pre-existing failures are triaged, not auto-blocking)
 - Pre-landing review finds ASK items that need user judgment
 - MINOR or MAJOR version bump needed (ask — see Step 4)
 - Greptile review comments that need user decision (complex fixes, false positives)
@@ -118,7 +118,11 @@ wait
 
 After both complete, read the output files and check pass/fail.
 
-**If any test fails:** Show the failures and **STOP**. Do not proceed.
+**If any test fails:** Do NOT immediately stop. Apply the Test Failure Ownership Triage:
+
+{{TEST_FAILURE_TRIAGE}}
+
+**After triage:** If any in-branch failures remain unfixed, **STOP**. Do not proceed. If all failures were pre-existing and handled (fixed, TODOed, assigned, or skipped), continue to Step 3.25.
 
 **If all pass:** Continue silently — just note the counts briefly.