[feature] enablement: ensure consuming repos ignore the .meshloop/ store #44

Background & Problem Statement

The first meshloop plan in a consuming repository creates the local store at <repo>/.meshloop/state.sqlite (default_db in crates/meshloop-cli/src/compose.rs:86). Nothing in the enablement or installation flow tells the target repository to ignore it. Meshloop's own .gitignore has /.meshloop/ and **/.meshloop/, but consuming repositories don't get that.

Seen on 0.3.0 in smota/holoself: after one meshloop plan, git status showed ?? .meshloop/. A broad git add . would have committed the SQLite store, with its WAL/SHM files, and its run history (objectives, task descriptions, attempt records) to a public repository. Worktrees are fine: default_worktree_base puts them in the sibling directory ../.meshloop-worktrees/<repo>, outside the repository.

docs/install.md:112 mentions where the database lives, but neither meshloop bundle --dest . nor the install steps add, suggest or check an ignore rule.

Proposed Solution

Make ignoring the store part of enabling Meshloop in a repository, without silently editing user files:

1. meshloop bundle --dest <repo> (the enablement step): check whether .meshloop/ is ignored (git check-ignore -q .meshloop/state.sqlite). If it isn't, either append a marked block to <repo>/.gitignore with a flag (for example --gitignore), or print the exact line to add and report it in the JSON output as gitignore: missing.
2. First store creation: when plan/run creates .meshloop/ inside a Git work tree and the path is not ignored, write .meshloop/.gitignore containing *. This is self-contained, never touches the user's root .gitignore, and protects the store even when the bundle step was skipped. Report it once on stderr.
3. meshloop doctor: add a check, e.g. store_ignored: true|false, with the remediation line.
4. Docs: add the ignore step to docs/install.md / docs/start.md next to the database location.

Requirements

• A fresh repository that runs meshloop plan never shows .meshloop/ as untracked.
• The root .gitignore is modified only with explicit consent (flag or prompt), and the block is idempotent and marked.
• doctor --json reports whether the store path is ignored.
• A custom --db path outside the work tree is not flagged.

Acceptance criteria

• Test: temporary Git repo, meshloop plan --fixture-only … → git status --porcelain does not list .meshloop/.
• Test: bundle --dest <tmp-repo> without the flag leaves .gitignore byte-identical and reports gitignore: missing. With the flag, it appends the block once, and a rerun makes no change.
• Test: doctor --json returns store_ignored: false before and true after.
• Install docs list the step.

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