feat(store): hierarchical database path resolution with per-project support

[Acharnite]

Summary

Replace the simple --db-or-default path logic with a 6-level hierarchical database path resolution chain. This eliminates the need for wrapper scripts or hardcoded paths when working across multiple projects.

Resolution chain (highest priority first)

Level	Source	Example
1	--db CLI flag	icm --db /tmp/test.db store ...
2	ICM_DB env var	ICM_DB=/tmp/icm.db icm recall ...
3	Global config [store].path	~/.config/icm/config.toml
4	Project-local .icm/config.toml [store].path	Git root auto-detection
5	Project-local .icm/memories.db	Auto-detected at git root (if file exists)
6	Platform default data directory	~/.local/share/icm/memories.db

Key changes

crates/icm-cli/src/main.rs (+165/−19):

• New resolve_db_path(cli_db, cfg) → PathBuf with the 6-level chain
• New detect_project_root() → Option<PathBuf> using git rev-parse --show-toplevel
• icm init --per-project now creates .icm/config.toml with [store] path = "memories.db"
• icm config shows the full resolution chain with source tracing (resolved path, config path, env var, project root, .icm/ state)
• open_store() simplified from open_store(db: Option<PathBuf>) to open_store(db: PathBuf) — resolution happens before the store is opened

config/default.toml (+11):

• Documents the full 6-level resolution order in the config header
• Explains icm init --per-project creates project-local config

OpenCode plugin improvements (plugins/opencode-icm.ts, +17/−10)

• Added NOISE_TOOLS set to skip extraction for Edit/Write/Question/todowrite calls (reduces noise)
• Increased EXTRACT_EVERY from 3 to 10 (reduces extraction frequency)
• Added cwd parameter to all ICM subprocess calls so the plugin respects per-project databases
• Fixed recall-project to use named flags (--project, --limit) instead of positional args

Documentation

• docs/architecture.md: New Database Path Resolution section with the full algorithm, priority flow diagram, and icm config output example
• docs/guide.md: Per-project setup instructions and resolution priority table
• README.md: Already updated with --per-project setup, ICM_DB env var mention, and per-project storage section

Backward compatibility

Fully backward compatible. The existing --db flag still works at the same priority. The default platform path (level 6) is unchanged. Existing setups see no behavioral difference.

Closes the gap where users had to set --db on every invocation or write wrapper scripts to use per-project databases.

[pszymkowiak]

Thanks for this, @Acharnite! Could you retarget this PR to develop (our integration branch — PRs to main fail the target-branch check) and rebase on the latest develop? The per-project .icm/config.toml + git-root resolution is a nice complement to the worktree project-detection fix we just merged (#235). Happy to review once it's rebased and CI is green.

[pszymkowiak]

Thanks for this — per-project memory (#321) is a genuinely useful feature and the resolution hierarchy (--db → \$ICM_DB → global config → project .icm/config.toml → project .icm/memories.db → default) is a sensible design. A few things need addressing before it can land:

1. Blocking — the branch is stale (pre-#301 multi-backend refactor)

develop has since moved open_store to the runtime-selected backend enum:

// develop
fn open_store(db: Option<PathBuf>, embedding_dims: usize) -> Result<Store>   // not SqliteStore

This PR reintroduces -> Result<SqliteStore> and the old open_store(db: PathBuf, …) signature, so it won't compile / will conflict. It also predates open_store_readonly (#263/#319) and open_maintenance (#313), which now resolve the same DB path — they'd need the new resolve_db_path wired in too, or per-project resolution silently won't apply to --read-only serve, doctor, and repair. Please rebase onto current develop and re-thread the resolution through all the openers.

2. Security — untrusted project .icm/config.toml can redirect where ICM writes

resolve_db_path auto-reads store.path from a project-local .icm/config.toml and honors absolute paths (if Path::new(path_str).is_absolute()). That means cloning/opening any repo that ships a .icm/config.toml can point ICM's SQLite DB at an arbitrary location on my machine — ICM then creates and writes a DB file there (potential overwrite / data loss / writing outside the project). Please either:

• restrict project-config paths to within the project root (reject absolute paths and .. escapes), and/or
• gate project-config auto-discovery behind an explicit opt-in.
  The .icm/memories.db-if-exists branch (4b) is fine since it's fixed under the project.

3. Reuse existing git detection

The codebase already detects the repo via project_from_path (git rev-parse --git-common-dir) for project tagging. detect_project_root adds a second git rev-parse --show-toplevel spawn on every resolution. Consider consolidating (and note this runs on latency-sensitive hook paths — walking up for .git/.icm in pure Rust avoids a subprocess and the hard git dependency).

Nits

• Tests: please add coverage for the resolution order (each tier), the absolute-path rejection, and the no-git fallback.
• config/default.toml doc comment references src/main.rs — the crate path is crates/icm-cli/src/main.rs.

Happy to re-review once it's rebased and the path-injection is bounded — the feature itself is welcome.