fix(plugin): restore OpenCode 1.3 loader compatibility

[NaNomicon]

Summary

Fixes #73 — opencode-mem was silently skipped by OpenCode ≥ 1.3.8 due to a plugin entrypoint/module-shape incompatibility.

Root Cause

OpenCode v1.3.x introduced a PluginModule contract: the plugin loader (readV1Plugin) now expects the module default export to be an object with a server property — { server: Plugin }. The previous opencode-mem@2.12.1 published dist/plugin.js with a bare function as the default export. The loader's isRecord(mod.default) check returned false, so it logged "No plugin targets found" and skipped the plugin entirely — without throwing an error.

Additionally, OpenCode v1.3.x resolves plugins via exports["./server"] in package.json. The published package had no exports map at all, so the loader fell back to main — but the module shape mismatch meant it was still rejected.

Consequence: Plugin hooks never fired → no memory saves, no web UI, /memory add had no visible effect (though user-prompts.db was modified by the module-level constructor).

Changes

File	Change
package.json	Add exports map with "." and "./server" entries; bump @opencode-ai/plugin ^1.0.162 → ^1.3.0 and @opencode-ai/sdk ^1.2.26 → ^1.3.0
src/plugin.ts	Replace bare default function export with { server: OpenCodeMemPlugin } satisfies PluginModule; add import type { PluginModule } for compile-time validation; remove stale shebang
tests/plugin-loader-contract.test.ts	Add regression guard: 4 assertions verifying exports map, default export shape, .server callable surface, and hook return values
bun.lock	Updated for dependency bumps

Verification

• bun run typecheck → exit 0 (no errors)
• bun run build → exit 0
• Regression guard: 4/4 tests pass
• Built artifact: typeof mod.default === "object", typeof mod.default.server === "function"
• Loader-parity smoke check: simulated OpenCode 1.3.11 readV1Plugin logic confirms isRecord(mod.default) === true → plugin would be loaded via v1 path (NOT skipped)

Backward Compatibility

• main: "dist/plugin.js" is preserved for loaders that fall back to main
• Named export OpenCodeMemPlugin is preserved
• Runtime behavior in src/index.ts is unchanged — only the module entrypoint shape and dependencies were updated
• OpenCode < 1.3.x (pre-PluginModule) is no longer supported by this package; the minimum required OpenCode version is 1.3.x

[NaNomicon]

After installing the local build and fighting my own environment, I got it working and believe this PR is enough to get opencode-mem to the working state with OpenCode v1.3.x. I did encountered some errors in the testing phase but I believe they're not related and opened follow-up issue about it. This PR will require the owner or someone with previous successful operations of the plugin to check before merge.

[tickernelz]

Bro you already have direct access to the repo.