refactor(widgets): collapse the duplicated Nerd Font toggle helpers

[zachthedev]

Five widgets each carried their own copy of the same four Nerd Font toggle
helpers: VimMode.ts, SandboxStatus.ts, RemoteControlStatus.ts,
VoiceStatus.ts and CompactionCounter.ts. The first four are byte-identical
once the format type name is normalized; CompactionCounter's differ only by
inlining its predicate. Net -163 lines.

Pure dedup, no behavior change.

shared/metadata.ts gains isNerdFontEnabled, setNerdFontFormat and
toggleNerdFont, each taking a NerdFontFormats config as a trailing argument.
That module already owned removeMetadataKeys, which removeNerdFont reduces to
a one-liner over, and CompactionCounter was already importing from it for its
hide flag while hand-rolling these lower in the same file.

Config-object-per-call rather than a factory, since it matches how
symbol-override.tsx threads SymbolSlot and nothing in shared/ uses a
factory. It also keeps canUseNerdFont lazy, which matters because two of the
predicates read item.rawValue.

Each widget keeps only its own canUseNerdFont, which is the genuinely
per-widget half:

Widget	Draws a glyph when
VimMode	format is icon-dash-letter, icon-letter or icon
SandboxStatus	format is glyph
RemoteControlStatus / VoiceStatus	format is icon, or icon-text outside raw value mode
CompactionCounter	format is the default

CompactionCounter had no such function; it inlined that predicate in three
places, including its keybind gate. It gets one as a named function, which
collapses all three.

Two things worth flagging:

• toggleMetadataFlag looks like it should serve toggleNerdFont and does not.
  It writes nerdFont: 'false', while all five widgets delete the key and
  collapse empty metadata to undefined. Reusing it would write junk into every
  user's settings.json. removeMetadataKeys is the exact match and is what this
  uses.
• SandboxStatus and VoiceStatus also carried a byte-identical config cwd
  resolver. Both now call resolveClaudeConfigCwd, which lives in
  claude-settings.ts next to the settings layering it feeds.

No test file is touched, which is the point: the existing suites pin the behavior
and still pass unchanged.

Tested: bun run lint clean; bun test 1866 pass, plus the
global-command-resolution failure main already has on this host and one hit
of the flaky fetchUsageData case.