Use the loaded supermemory config file in install and status

[Chebaleomkar]

Fixes #91

Problem

The plugin loads supermemory.jsonc before supermemory.json, but the CLI only knew about supermemory.json. With a .jsonc config (the file the README tells users to create), status reported the working key as not configured, and install treated the setup as fresh and wrote a stray supermemory.json containing a copy of the API key and settings that never take effect.

Fix

• src/config.ts: remember which file was actually loaded and export it as CONFIG_FILE. It falls back to supermemory.json only when neither file exists, so fresh installs behave exactly as before.
• install: apply its defaults to that file with jsonc-parser (via the existing applyModification helper in opencode-config.ts), so user comments, formatting, and settings are preserved instead of the file being rewritten with JSON.stringify. This lives on the CLI side, so jsonc-parser does not enter the plugin runtime bundles (v2 index.js stays at ~141.7 KB).
• status: parse the config as JSONC when reporting the key source.
• Behaviour change: if the existing config can't be parsed, install now prints ⚠ Could not parse <file>; left it unchanged. instead of overwriting the user's file with defaults.

No effect on the plugin inside OpenCode sessions: CONFIG_FILE is only used by the CLI. Users who authenticate via login or SUPERMEMORY_API_KEY, or who keep their config in supermemory.json, see no difference. Stray supermemory.json files created by earlier versions are left alone; #91 tells affected users they can delete them.

Before / after

Same repro as #91 (sandboxed HOME, fake key, only supermemory.jsonc present):

# main
API key: sm_fak...1234 (not configured)
$ install --no-tui && ls ~/.config/opencode | grep supermemory
supermemory.json          <- new file with a copy of the key
supermemory.jsonc

# this branch
API key: sm_fak...1234 (~/.config/opencode/supermemory.jsonc)
$ install --no-tui && ls ~/.config/opencode | grep supermemory
supermemory.jsonc         <- untouched, comment preserved

Testing

• New unit tests in src/services/opencode-config.test.ts for applyInstallDefaults: keeps comments and user settings, leaves an existing captureEveryNTurns untouched, writes fresh-install defaults, returns null for unparseable input.
• bun run typecheck clean, bun test 37 pass.
• Ran the built CLI end to end with a sandboxed HOME on Windows 11:

Config on disk	install result	status key source
only supermemory.jsonc	no stray .json; file and comments unchanged	…/supermemory.jsonc
none (fresh)	creates supermemory.json with recallMode: "direct", captureEveryNTurns: 0 (unchanged from main)	not configured
only supermemory.json (legacy)	adds captureEveryNTurns: 3 (unchanged from main)	…/supermemory.json
unparseable supermemory.jsonc	warns, file left as is	not configured