chore: add changelog (#284)

## Changes
- **Added `CHANGELOG.md`** — Initial changelog documenting recent
user-facing changes including:

- **Added `.claude/skills/update-changelog.md`** — A skill guide for
maintaining the changelog.

- **Updated `CLAUDE.md`** — Added a new "Changelog" section documenting
the requirement to run `/update-changelog` for user-facing changes

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: branchseer

.claude/skills/update-changelog.md

@@ -0,0 +1,41 @@
+---
+description: Update CHANGELOG.md with a new entry for the current change
+user_invocable: true
+---
+
+# Update Changelog
+
+Add a new entry to `CHANGELOG.md` for the change being made in the current branch.
+
+## Instructions
+
+1. Read `CHANGELOG.md` to understand the current format.
+2. Determine the appropriate category for the change:
+   - **Added** — new user-facing feature or capability
+   - **Changed** — modification to existing user-facing behavior
+   - **Removed** — removal of user-facing feature or option
+   - **Fixed** — bug fix affecting users
+   - **Perf** — performance improvement noticeable to users
+3. Write a concise, user-facing description. Focus on what changed from the user's perspective, not implementation details.
+4. Include a PR link in the format `([#NNN](https://github.com/voidzero-dev/vite-task/pull/NNN))`. If the PR number is not yet known, leave a `([#???](https://github.com/voidzero-dev/vite-task/pull/???))` placeholder.
+5. Insert the new entry at the **top** of the existing list in `CHANGELOG.md` (newest first).
+6. If the current change is closely related to an existing entry (e.g., multiple PRs contributing to the same feature or fix), group them into a single item with multiple PR links rather than adding a separate entry.
+
+## What NOT to include
+
+Do not add entries for:
+
+- Internal refactors with no user-facing effect
+- CI/CD changes
+- Dependency bumps
+- Test-only fixes (flaky tests, test infrastructure)
+- Documentation changes (CLAUDE.md, README, etc.)
+- Chore/tooling changes
+
+The changelog is for **end-users only**.
+
+## Entry format
+
+```
+- **Category** description ([#NNN](https://github.com/voidzero-dev/vite-task/pull/NNN))
+```

CHANGELOG.md

@@ -0,0 +1,7 @@
+# Changelog
+
+- **Changed** default untracked env patterns to align with Turborepo, covering more CI and platform-specific variables ([#262](https://github.com/voidzero-dev/vite-task/pull/262))
+- **Added** `--log=interleaved|labeled|grouped` flag to control task output display: `interleaved` (default) streams directly, `labeled` prefixes lines with `[pkg#task]`, `grouped` buffers output per task ([#266](https://github.com/voidzero-dev/vite-task/pull/266))
+- **Added** musl target support (`x86_64-unknown-linux-musl`) ([#273](https://github.com/voidzero-dev/vite-task/pull/273))
+- **Changed** cache hit/miss indicators to use neutral symbols (◉/〇) instead of ✓/✗ to avoid confusion with success/error ([#268](https://github.com/voidzero-dev/vite-task/pull/268))
+- **Added** automatic skip of caching for tasks that modify their own inputs ([#248](https://github.com/voidzero-dev/vite-task/pull/248))

CLAUDE.md

@@ -135,6 +135,10 @@ All code must work on both Unix and Windows without platform skipping:
 - Platform differences should be handled gracefully, not skipped
 - After major changes to `fspy*` or platform-specific crates, run `just lint-linux` and `just lint-windows`
 
+## Changelog
+
+When a change is user-facing (new feature, changed behavior, bug fix, removal, or perf improvement), run `/update-changelog` to add an entry to `CHANGELOG.md`. Do not add entries for internal refactors, CI, dep bumps, test fixes, or docs changes.
+
 ## Quick Reference
 
 - **Task Format**: `package#task` (e.g., `app#build`, `@test/utils#lint`)