chore: bump version to 3.0.1 + changelog entry

Atomic bump across all four manifests:
- SKILL.md (root)
- skills/last30days/SKILL.md (internal spec)
- .claude-plugin/plugin.json
- gemini-extension.json

CHANGELOG entry documents the skill-upload packaging fix, vendor/ removal,
legacy plans/ removal, and the new scripts/build-skill.sh builder.

CHANGELOG.md

@@ -5,6 +5,24 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.0.1] - 2026-04-14
+
+### Fixed
+
+- **Skill upload packaging** - `scripts/build-skill.sh` produces a claude.ai-upload-ready `.skill` file that fits under the 200-file cap. Previously, zipping the repo hit 406 files and the "Upload skill" UI rejected it outright.
+- **SKILL.md description length** - trimmed from 228 to 167 chars (Anthropic caps descriptions at 200).
+
+### Removed
+
+- Unused root `vendor/` directory (215 files from an accidental commit in PR #48 - the real vendored X client lives at `scripts/lib/vendor/bird-search/`).
+- Legacy top-level `plans/` directory (superseded by `docs/plans/`; both plans described work that was already shipped in v3).
+
+### Added
+
+- `.gitattributes` with `export-ignore` entries so `git archive` drops tests, docs, fixtures, assets, historical manifests, and internal skill subdirs. Mirrors Anthropic's canonical `package_skill.py` exclusions.
+- `scripts/build-skill.sh` - one-command path to produce `dist/last30days.skill` with a single top-level `last30days/` folder, defensive `=200` file check, and dirty-tree refusal.
+- `README.md` section documenting the claude.ai skill upload workflow.
+
 ## [3.0.0] - 2026-04-11
 
 ### Highlights