chore(skills): add commit-task-tags skill for kanban TG trailers

Documents the TG-<NUMBER> #<state> commit message trailer convention:
state semantics (new, ready, in-progress, ready-for-test, done), rules
for multi-commit epics, and a helper script for amending tags during
interactive rebase.

.pi/skills/commit-task-tags/SKILL.md

@@ -0,0 +1,99 @@
+---
+name: commit-task-tags
+description: Manage kanban task tags (TG-<NUMBER> #<state>) in git commit messages. Use when creating, squashing, or rebasing commits to ensure task state trailers are correct.
+---
+
+# Commit Task Tags
+
+This project tracks kanban board tasks inside git commit messages using trailer
+lines in the format:
+
+```
+TG-<NUMBER> #<state>
+```
+
+Multiple trailers may appear in a single commit (one per related task). Trailers
+go at the bottom of the commit body, separated from the prose by a blank line.
+
+## States
+
+| State | Meaning |
+|-------|---------|
+| `new` | Task created on the board; no work started yet. |
+| `ready` | Task is defined and ready to be picked up. |
+| `in-progress` | This commit contributes to the task, but the full task/epic is **not** yet implemented. Use for every intermediate commit. |
+| `ready-for-test` | The **full implementation** of the task/epic is completed across all its commits. Place on the final commit of the task. |
+| `done` | Property of the **full task**, not of an individual commit. Reserved for final board confirmation after testing. **Never** use `#done` in a code commit. |
+
+### Key rules
+
+1. **`#done` is not for commits.** A commit can at most mark a task
+   `#ready-for-test`. The `#done` state is set on the kanban board after
+   verification, not in git.
+
+2. **Multi-commit epics use `#in-progress` then `#ready-for-test`.** Every
+   intermediate commit for a task carries `#in-progress`. Only the final commit
+   that completes the implementation switches to `#ready-for-test`.
+
+3. **Single-commit tasks use `#ready-for-test`.** If a task is fully implemented
+   in one commit, that commit carries `#ready-for-test` (not `#done`).
+
+4. **One task may span many commits.** Add the same `TG-<N>` trailer to every
+   commit that touches that task's work, updating the state as appropriate.
+
+## Example commit
+
+```
+feat(cloud_point): stereo rectification and point cloud pipeline
+
+- StereoRectifier wrapping cv::stereoRectify
+- PointCloudBuilder with depth filtering
+- E2E synthetic-scene test
+
+TG-9 #ready-for-test
+TG-2 #in-progress
+```
+
+## Adding tags to existing commits
+
+### During interactive rebase (recommended)
+
+Use `git rebase -i` with `edit` stops, then amend each commit:
+
+```bash
+# Strip old TG lines and append new ones in one command:
+git log -1 --format=%B \
+  | sed '/^TG-[0-9]/d' \
+  | { cat; printf '\nTG-<N> #<state>\n'; } \
+  | git commit --amend --no-verify -F -
+git rebase --continue
+```
+
+> **Avoid `reword`** with a shared `GIT_EDITOR` script — it can shift tags by one
+> commit. Use `edit` stops with explicit `git commit --amend` instead.
+
+### Helper script
+
+A reusable script lives at `scripts/tag-commit.sh` in this skill directory.
+
+```bash
+# At a rebase edit stop, add or replace tags:
+../scripts/tag-commit.sh "TG-5 #ready-for-test" "TG-2 #in-progress"
+git rebase --continue
+```
+
+The script strips any existing `TG-*` lines from the current commit message,
+appends the supplied trailers, and amends the commit.
+
+## Squashing commits
+
+When squashing many commits into fewer logical commits, reassign task tags to
+the resulting squashed commits following the same state rules. After squashing:
+
+1. Identify which tasks each squashed commit covers.
+2. Mark intermediate squash commits `#in-progress` for tasks that continue in
+   later squash commits.
+3. Mark the final squash commit for a task `#ready-for-test`.
+
+Use `git reset --hard <group-end>` + `git reset --soft <prev-group-commit>` to
+snapshot each group's tree, then `git commit` with the appropriate trailers.

.pi/skills/commit-task-tags/scripts/tag-commit.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+# tag-commit.sh — Add or replace TG-<NUMBER> #<state> trailers on the current commit.
+#
+# Usage (at a rebase edit stop or any HEAD you want to amend):
+#   ./tag-commit.sh "TG-5 #ready-for-test" "TG-2 #in-progress"
+#
+# Strips existing TG-* lines, appends the given trailers, and amends the commit.
+
+set -eu
+
+if [ "$#" -eq 0 ]; then
+  echo "Usage: $0 \"TG-<N> #<state>\" [\"TG-<N> #<state>\" ...]" >&2
+  exit 1
+fi
+
+# Build the trailer block from arguments.
+trailers=""
+for tag in "$@"; do
+  trailers="${trailers}${tag}"$'\n'
+done
+
+# Strip existing TG-* lines, append new trailers, amend commit.
+git log -1 --format=%B \
+  | sed '/^TG-[0-9]/d' \
+  | { cat; printf '\n%s' "$trailers"; } \
+  | git commit --amend --no-verify -F -