Flatten the repo: move everything out of app/ to the root

Now that the CLI and the Next.js app are one package, nesting it inside
app/ served no purpose - the repo root itself becomes the published
npm package. Merges app/.gitignore and app/README.md into the root
versions, drops the now-duplicate app/LICENSE, and updates path
references (README, docs/ARCHITECTURE.md, docs/CONFIG_REFERENCE.md,
package.json's repository.directory) that assumed the app/ nesting.

Also fixes a real bug this surfaced: the in-app docs viewer resolved
docs/ relative to process.cwd(), which only worked by accident when the
CLI happened to be invoked from app/'s parent directory. A first attempt
at fixing it with import.meta.dirname broke instead, for the same
cross-module-graph reason config-path resolution already documented -
Next compiles Route Handlers through a separate module graph that
doesn't preserve source-relative import.meta paths. Fixed by exposing
the app root via TRIGGERSHELL_APP_ROOT (set once in server.ts, where
import.meta *does* resolve correctly), the same pattern already used
for TRIGGERSHELL_CONFIG_PATH.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -1,8 +1,8 @@
 # Architecture
 
 ```
- triggershell (Node CLI, src/cli)               app/ (Next.js, all server logic)
- ───────────────────────────────                ──────────────────────────────
+ triggershell (Node CLI, src/cli)               server.ts + src/ (Next.js, all server logic)
+ ───────────────────────────────                ─────────────────────────────────────────
  triggershell start                              server.ts (custom Node server)
    1. resolve + validate the config (loadConfig)    ├─ Next.js request handler (pages, API routes)
    2. check the port is free                        ├─ ws.WebSocketServer on /ws/runs
@@ -24,7 +24,7 @@
 
 ## Why a custom Node server
 
-Next.js Route Handlers can't host a persistent WebSocket server, so `app/server.ts` wraps Next's
+Next.js Route Handlers can't host a persistent WebSocket server, so `server.ts` wraps Next's
 request handler in a plain `http.createServer` and attaches a `ws.WebSocketServer` via the
 `upgrade` event, scoped to `/ws/runs` with its own auth check (Route Handlers get auth via
 `next/headers`'s `cookies()`, which isn't available on a raw `http.IncomingMessage`).
@@ -100,4 +100,4 @@ Every server file that reads the config/DB at request time (`getConfig()`, `getD
 `requireAuth()`) sets `export const dynamic = "force-dynamic"`. Without it, `next build` tries to
 statically prerender pages like `/` at build time, which fails because there's no config file to
 read yet (the config only exists at `triggershell start` runtime, in the user's own project
-directory, not `app/`'s).
+directory, not the package's).