Add Brave template (packed Chromium theme)

[kurtlieber]

Template

• App: Brave
• Template id (directory): brave
• New template
• Update to an existing template

What it themes

Brave / Chromium chrome UI via a packed theme (manifest.json + generated
solid PNGs). Noctalia renders the manifest to
$XDG_CACHE_HOME/noctalia/brave-theme/manifest.json. The hook installs
frame / toolbar / NTP / tab-background images next to it at
$XDG_DATA_HOME/noctalia/brave-theme so Linux chrome actually paints
(color-only packs often leave the frame and toolbar unpainted).

Surfaces: window frame, tabs, toolbar, bookmark text, omnibox, NTP
background / text / link.

Settings checkboxes and Leo accents are not in Chromium's overwriteable
theme table. If Brave is fully quit, the hook also writes
browser.theme.color_scheme and browser.theme.user_color (primary seed).
It never writes Preferences while Brave is running.

Related but distinct from #84 (ungoogled-chromium): this targets Brave's
profile path and installs the PNG fill images.

Testing

Tested as a user template first (Noctalia v5.0.0).

• App version tested: Brave 151.1.93.136
• Applied a dark theme and confirmed the app picked it up
• Applied a light theme and confirmed the app picked it up
• Re-applied twice and the app config is still correct (hooks are idempotent)

Screenshot below is the current light palette. First-time step: load unpacked
from brave://extensions → Developer mode →
~/.local/share/noctalia/brave-theme. After that, palette changes update the
pack; reload with Developer mode → Update (or restart Brave).

Screenshots

Hooks

• What the hook does: writes solid PNGs beside the rendered manifest so
  Linux paints frame/toolbar/NTP; prints first-time load-unpacked help; if
  Brave is stopped, syncs color_scheme / user_color. Optional
  backup / restore verbs snapshot Preferences once.
• It is idempotent: running it twice does not duplicate lines or corrupt the config.
• It fails loudly (non-zero exit, message on stderr) when the app's config is missing.
• It downloads nothing and executes nothing it did not ship in this directory.
• It touches only this app's own config.

Checklist

• The directory name matches the [catalog.brave] id in template.toml.
• category is one of: ai, audio, browser, chat, compositor, editor, gaming, launcher, system, terminal, misc.
• Every input_path names a file that exists in this directory.
• No generated output or app-specific personal config is committed.