Use Tcode consistently as the product display name

[Tryanks]

The product name now appears as Tcode in the shared shell, native menu/window captions, Android app label, iOS permission prompts, web startup/accessibility text, both locales, provider display titles and warnings, MCP help, Markdown exports, and user documentation. Commands, crate names, protocol/server IDs, URLs, filenames, storage keys and data directories retain tcode.

Reuses the existing app.name locale key for standalone shared-UI names instead of adding a competing constant or locale key. Existing packaging already uses Tcode for macOS/iOS display names and release notes; those technical packaging references remain unchanged. Headless CLI references remain command names. No new abstraction or text-mirroring test was added. The existing Markdown export fixture and provider-status expectation were updated for the visible wording; JSONL compatibility coverage remains intact.

Validation so far:

• cargo fmt --all --check and git diff --check: pass.
• cargo test -p tcode-services --locked export::: 3 passed.
• cargo test -p tcode-ui --locked i18n::: 3 passed, including locale parity.
• node --test crates/web/static/auth.test.mjs: 2 passed.
• cargo clippy --workspace --all-targets --locked -- -D warnings: final rerun passed after restoring the required app title field with app.name.
• cargo build --workspace --locked: passed. The debug link emits an existing-size warning about __eh_frame; Cargo also reports future incompatibility in dependency block 0.1.6.
• cargo test --workspace --locked: passed; suite summaries report 1,083 passes and 5 explicit ignores (includes child-process fixture summaries), including all 392 UI tests.
• cargo-machete 0.9.2: passed. This installation's cargo machete wrapper treats the subcommand as a directory; direct invocation works. GitHub Dependency hygiene also passed.
• RUSTFLAGS='-D warnings' IPHONEOS_DEPLOYMENT_TARGET=26.0 cargo check -p tcode-ios --target aarch64-apple-ios-sim --locked: passed.
• RUSTFLAGS='-D warnings' cargo check -p tcode-web --target wasm32-unknown-unknown --locked: passed.
• RUSTFLAGS='-D warnings' CARGO_NDK_PLATFORM=26 cargo ndk -t arm64-v8a check -p tcode-android --locked: local toolchain unavailable (no Android NDK found). GitHub Mobile and web checks passed on the same commit.
• python3 .github/scripts/test_ci_scope.py: passed (13 tests, 9 explicitly skipped).
• Actual macOS GUI verification completed on this commit in the copied review app with TCODE_DATA_DIR=/tmp/377-evidence/profiles/light. Fresh isolated startup AX reports window Tcode, never app.name; sidebar and empty-project description show Tcode. English and Chinese General Settings prose was inspected in both themes at normal and narrow widths, with no branding-related clipping.
• Local GUI evidence: /tmp/377-evidence/light-wide-startup.png; {light,dark}-{wide,narrow}-settings.png; zh-{light,dark}-{wide,narrow}-settings.png; final-window-ax.txt. Normal captures are approximately 1152×768 (the default 1200×800 window rendered by the capture tool); narrow captures are 668–669×800. These local paths are for lead inspection, not hosted PR attachments.
• Review app was quit and no /tmp/377-evidence process remains. GUI slot released. Native phone launch screens, OS notification dialogs and the browser canvas were not separately driven; native metadata/source checks and passing mobile/Web CI cover those build surfaces.
• All six GitHub checks passed: Plan CI scope, Dependency hygiene, macOS arm64, Linux x64, Windows x64, and Mobile and web checks. Awaiting lead acceptance; not merged.

The repository description is empty and remains unchanged.

Closes #377.