chore: revert PR #180 (pin plugin to CLI v3.0) — redo after CLI GA

[kengio]

Reverts #180. Will redo after CLI v3.0.0 GA.

Why now

PR #180 declared a hard `requires.cli: '>=3.0.0-alpha.1'` and bumped the plugin version 2.4.13 → 3.0.0-alpha.1 ahead of the CLI's actual GA. Three issues surfaced in practice:

1. The v3 CLI is still pre-GA (v3.0.0-alpha.5 in flight as of today). Anyone on a clean install picks up the plugin via `vault-sync` and then trips the version check until they manually update the CLI.
2. The plugin itself still works against both Bun v2.3.3 and the Rust alpha series — there's no skill that requires v3-only behaviour today.
3. Coupling plugin 3.0.0-alpha.1 to CLI 3.0.0-alpha.1 confuses the versioning story: plugin alpha + CLI alpha both at .alpha.1, drifting separately as each repo bumps.

Plan

• This PR restores the pre-feat: pin plugin to CLI v3.0 (Rust) #180 plugin.json shape (no `requires.cli` field, no `version: 3.0.0-alpha.1`) and bumps the plugin to v2.4.14 to record the revert.
• The CLI-v3 pin will be re-applied as a follow-up — likely `requires.cli: '>=3.0.0'` — once the CLI's v3.0.0 GA tag ships.

Diff

• `.claude/plugins/onebrain/.claude-plugin/plugin.json`: `version` back to `2.4.14`, `requires.cli` field removed.
• `PLUGIN-CHANGELOG.md`: drop the `v3.0.0-alpha.1` entry, add a v2.4.14 entry documenting the revert.

Test plan

• `plugin.json` parses as valid JSON
• `PLUGIN-CHANGELOG.md` frontmatter `latest_version` matches `plugin.json` `version`
• No skill or instruction in the plugin actually requires CLI v3-only behaviour today (verified by audit summarised in PR feat: pin plugin to CLI v3.0 (Rust) #180 itself — all 13 subcommand argv shapes are still backwards-compatible with the Bun CLI)