fix(skills): use absolute paths in start-sprint for worktree safety

The skill used bare relative paths like db/connectors/ticket which
fail when the shell CWD doesn't match the worktree root. Now requires
resolving REPO_ROOT via git rev-parse --show-toplevel first.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/skills/start-sprint/SKILL.md

@@ -14,6 +14,24 @@ allowed-tools: Bash, Read, Grep, Glob
 Prepare a team branch for sprint work: sync with main, load the sprint
 briefing, and present actionable next steps.
 
+## Path resolution (CRITICAL)
+
+This project uses **git worktrees**. Each team branch is a separate directory.
+All file paths MUST be resolved from the worktree root, never guessed.
+
+**First**, resolve the repo root and store it for all subsequent commands:
+```bash
+REPO_ROOT="$(git rev-parse --show-toplevel)"
+```
+
+Then use `$REPO_ROOT` as a prefix for every path in this skill:
+- Ticket CLI: `"$REPO_ROOT/db/connectors/ticket"`
+- Sprint briefings: `"$REPO_ROOT/docs/sprints/sprint-N/<team>.md"`
+- Decision files: `"$REPO_ROOT/decisions/*.md"`
+
+**Never use bare relative paths** like `db/connectors/ticket` — they break
+when the shell's CWD doesn't match the worktree root.
+
 ## Workflow
 
 ### 1. Determine the team
@@ -38,7 +56,7 @@ If the merge has conflicts, report them and stop — do not force-resolve.
 ### 3. Find the active sprint
 
 ```bash
-db/connectors/ticket sprint --active
+"$REPO_ROOT/db/connectors/ticket" sprint --active
 ```
 
 Extract the sprint ID and name from the JSON output. If no active sprint,
@@ -46,9 +64,9 @@ report that and stop.
 
 ### 4. Read the sprint briefing
 
-Read `docs/sprints/sprint-N/<team>.md` where N is the sprint ID and team
-matches the branch name. If the branch is `server` or `client`, use that
-directly. For other branches, check if a matching briefing exists.
+Read `$REPO_ROOT/docs/sprints/sprint-N/<team>.md` where N is the sprint ID
+and team matches the branch name. If the branch is `server` or `client`, use
+that directly. For other branches, check if a matching briefing exists.
 
 Also check for a `joint.md` briefing — joint tasks involve both teams and
 should be mentioned.
@@ -57,7 +75,7 @@ should be mentioned.
 
 For each ticket listed in the briefing, run:
 ```bash
-db/connectors/ticket show <id>
+"$REPO_ROOT/db/connectors/ticket" show <id>
 ```
 
 Identify which tickets are actionable now (no open blockers) vs blocked.
@@ -79,5 +97,5 @@ Output a summary:
 
 Then mark the first actionable ticket as `in_progress`:
 ```bash
-db/connectors/ticket status <id> in_progress
+"$REPO_ROOT/db/connectors/ticket" status <id> in_progress
 ```