release(app): 0.4.0, bundling core v1.1.12

[fujibee]

Version bump for the app 0.4.0 release. Both halves of the version state in one PR, since splitting them is how 0.1.5 shipped with the app version left behind.

app/src-tauri/tauri.conf.json   0.3.0  -> 0.4.0
app/package.json                0.3.0  -> 0.4.0
app/src-tauri/Cargo.toml        0.3.0  -> 0.4.0
app/src-tauri/Cargo.lock        0.3.0  -> 0.4.0
app/AGMSG_CORE_REF              v1.1.9 -> v1.1.12

Why MINOR

Both app changes since app-v0.3.0 are features:

• 94704fd drag files onto a pane to insert their path (feat(app): drag files onto a pane to insert their path #481)
• 3f87d60 render terminals via WebGL, attached only to the active pane (feat(app): render terminals via WebGL, attached only to the active pane #446)

That is the whole scope — git log app-v0.3.0..main -- app/ returns exactly these two.

Assertions

Re-ran the release checklist's version assertions after the edit:

ASSERT A  tauri.conf 0.4.0 != latest app tag 0.3.0   pass
ASSERT B  AGMSG_CORE_REF v1.1.12, tag present on origin (6248bb0)   pass

v1.1.12 exists on origin, so the pin resolves rather than pointing at a tag that has not landed yet.

Verification

bundle-core.sh    fetched v1.1.12, bundled agmsg-core, resources VERSION reads 1.1.12
pnpm test         8 files, 179 tests passed

One note on the test run: the first attempt reported 145 passed with one suite failing to load — @xterm/addon-webgl was missing from a stale node_modules. It is declared in package.json and present in the lockfile, so pnpm install --frozen-lockfile resolved it; nothing in this PR caused it. Worth recording because the failing count still looked like a pass at a glance: 34 tests were hidden behind the load error.