feat: add Font Awesome Free icons + Google Fonts resolver preset; fix…

[eigger]

… third-party licensing

Licensing fixes (see conversation review)

• Remove fonts/ppb.ttf: origin/license could not be verified, a real risk for a font shipped in a published PyPI package.
• Add NOTICE + LICENSE-APACHE-2.0: the rendering engine (registry dispatch + element handlers) was originally adapted from OpenEPaperLink's Home Assistant Integration (imagegen module, Apache-2.0) and has since been substantially rewritten/extended. Apache-2.0 Section 4 requires this attribution to travel with derivative works, regardless of how much the code has since changed.
• pyproject license -> "MIT AND Apache-2.0" (SPDX expression, PEP 639); the wheel now ships LICENSE/LICENSE-APACHE-2.0/NOTICE under dist-info/licenses, verified by a CI build-step assertion.
• Document bundled-asset licenses (MDI: Apache-2.0, Noto Sans KR: OFL-1.1) with full license texts co-located next to each asset.

New: Font Awesome Free as a second icon set

• icon/rich_text/legend now accept "fa:name" (auto solid > regular > brands), or a forced style via "fas:"/"far:"/"fab:" — alongside the existing "mdi:" default (unchanged, backward compatible).
• Bundled: fontawesome-free-{solid,regular,brands}.otf + a metadata file trimmed from upstream's icons.json (name/codepoint/styles/aliases only; 149 KB vs the 4.5 MB raw file) via the new scripts/build_fontawesome_assets.py (dev tool, not shipped). Only Free-tier icons are included.
• Licensed under SIL OFL 1.1 (fonts) / CC BY 4.0 (icons); full text bundled at icons/LICENSE-FONTAWESOME and referenced from NOTICE.
• media.py gains a single resolve_icon(value, icons_dir, size) dispatcher used by icon/rich_text/legend, replacing three separate mdi_char/mdi_font call sites.

New: google_fonts_resolver preset in imagespec.resolvers

• A caching_resolver preset over GOOGLE_FONTS_SOURCES — verified OFL-1.1 download URLs (google/fonts repo's ofl/ directory) for scripts the bundled Noto Sans KR doesn't cover: Japanese, Simplified/Traditional Chinese, Arabic, Thai, plus a broader Latin/Cyrillic/Greek family. Downloads once, caches to disk, same as caching_resolver — avoids bundling more fonts by default (keeps the wheel lean, avoids re-litigating font licenses per addition).

Tests: 128 passing (was 97) — new coverage for FA icon resolution (auto-style, forced-style, aliases, error paths), resolver presets, and existing regression tests updated to not depend on the removed ppb.ttf.

Verified: full wheel build inspected directly — new assets and license files land in the right places (dist-info/licenses/ vs package data), scripts/ ships in the sdist only (dev tool, not installed), twine check passes.