refactor: prune dead code (ProgressBar, parseSize dup, unused MoEngine facade methods)

[caezium]

A /prune audit of the repo. Headline: the codebase is clean — the engine
fold (#48/#71) left almost nothing behind, no unused deps, no dead files. This
PR removes the only three confirmed findings. −104 net lines, 6 files.

1. Remove dead ProgressBar view (b514d6e)

Unreferenced SwiftUI View in StatusView.swift — zero call sites anywhere
(progress UI uses IndeterminateBar / LowSpaceBar / count-up heroes).

2. Dedupe size-string parsing into Fmt.parseSize (55c8be0)

MoleClient.parseSize and CleanList.parseSize were near-identical 1024-based
parsers. Consolidated into one canonical Fmt.parseSize (the inverse of
Fmt.bytes); both keep their public names as thin forwarders, so all call
sites and both test suites are unchanged. The canonical is the superset
(raw-number fallback), so every existing assertion still holds.

3. Drop unused MoEngine.stream() / runElevatedClassified() (8e15bfc)

Both facade methods were production-unused: OperationFlow takes the streaming
port via the exposed MoEngine.shared.streamPort, and elevation runs through
MoleCLI.runElevatedClassified. They were exercised only by MoEngineTests.
Removed them plus the now-orphaned privilegeBroker dependency and the
MoLocator.locateTrusted() seam they alone used — no new dead code left behind.
The 3 deleted elevation tests are fully covered against the production path
by PrivilegeBrokerTests (launchFailed / authCancelled / exited) and
MoleCLITests ("trusted lookup must never come from PATH"). Docs updated.

Verification

• Adversarial multi-agent review (behavior, compile/strand, coverage): green.
• All changed files pass swiftc -parse; zero dangling refs to removed symbols.
• ⚠️ Build + full test suite not run locally (disk/sandbox limits) — relying
  on CI to run the gate.

No behavior change intended.