fix(memory): normalize readonly SQLite URI paths

[Grivn]

What

• Resolve the readonly database filename to an absolute filesystem path before constructing its SQLite file URI. Put Windows drive letters in the URI path (file:///C:/...), preserving URI escaping for spaces, Unicode, #, and %.
• Keep mode=ro, immutable=1, and the existing readonly mutation guards. No fallback to a writable connection, schema migration, or file-format change.
• Add real SQLite storage and recall regressions for absolute and relative paths, plus drive-relative paths on Windows. Verify successful queries, rejected direct SQL writes, unchanged database bytes (including recall counters/oplog), and absent WAL/SHM/journal files.
• Extend native Windows CI to run the Memory command and storage tests. Add built-CLI E2E coverage and document filesystem-path handling in English and Chinese.

Why

Closes #123.

The readonly URI construction introduced by #119 passes a Windows filename such as C:/.../mnemon.db directly to url.URL.Path. It serializes as file://C:/..., turning the drive into an invalid SQLite URI authority. Relative directory paths produce the same problem on other platforms. The driver reports the open failure as SQL logic error: out of memory (1) even for a tiny database.

SQLite's URI rules require the Windows drive to be part of the absolute path and drive-relative filenames to be resolved before conversion.

Normalize the path and retain the readonly snapshot contract so downstream callers, including dsh-mnemon's browse/metadata paths, do not need to remove --readonly and allow incidental writes.

Validation

Local validation ran on macOS arm64 with Go 1.25.4.

• Confirmed the new storage and recall relative-path regressions fail on unchanged master with the reported SQLite error and pass with this fix.
• make test passes, including go vet ./... and all deterministic packages.
• go test -race -shuffle=on ./internal/memory/store ./cmd/memory -count=3 passes.
• bash scripts/e2e_test.sh passes all 167 assertions, using the built CLI and synthetic data with the optional embedding endpoint disabled.
• CI run 33414798078 passes for commit 7bc609b5fbd609e68e88e3ea842307226af41c12:
  • Linux: the full deterministic suite.
  • Native Windows amd64 / Go 1.24.6: go build -o mnemon.exe . and go test ./cmd ./cmd/agency ./cmd/memory ./internal/memory/store -count=1, including the drive-letter and drive-relative regression cases.

The broader Agency daemon/process/Docker integration tier and paid-provider live tier were not run; those boundaries are unchanged.

Release-note impact

Release preparation includes the v0.2.7 entry in CHANGELOG.md.

Fix --readonly recall failing on Windows drive-letter paths and on relative --data-dir paths. Readonly recall continues to preserve the immutable snapshot without updating counters/oplog or creating sidecars. The existing limitation for databases actively changed by another process is unchanged.

Checklist

• Deterministic tests pass (make test)
• Relevant CLI E2E and Memory race boundaries pass (see validation above)
• New/changed behavior is covered by tests
• Documentation updated in English and Chinese
• User-facing release-note impact described in this PR