feat(dev-fkeys): revert projectile cache on failed-and-modified compile

Without this, a one-off typo at projectile's compile/test/run prompt poisons the per-project cache: every subsequent invocation pre-fills the broken value. I hit it during the Phase 2a live-test, where projectile's "All tests" prompt was replaying `go test ../.` and there was no clean way to get the prior known-good back.

Three pieces of machinery, all in `dev-fkeys.el`:

`cj/--projectile-capture-cmd' captures the current cached cmd at the project root before each invocation, stashing a plist with :map / :root / :prior in `cj/--projectile-revert-state'.

`cj/--projectile-revert-on-fail' is a `compilation-finish-functions' hook that reads that state. If the compile failed AND the cmd was modified from the captured prior value AND the prior was non-nil, it puts the prior back in projectile's cmd-map. Test-fails-because-of-real-bug (cmd unchanged through the run) leaves the cache alone. The hook self-removes on first invocation regardless of outcome and clears the state.

`cj/--projectile-around-revert' is the around-advice that wires the two together. I added the advice to all three projectile cmd-runners — `projectile-compile-project', `projectile-test-project', `projectile-run-project' — so the auto-revert applies whether the user invoked via F4 / F6 or directly via `M-x'.

Plus the manual escape-hatch: `cj/projectile-reset-cmds' clears compile/test/run cache for the current project. Bound to `C-; P' under the personal keymap. Use when projectile's auto-derived default was wrong from the start and you want to start fresh — the next F4 / F6 invocation re-derives projectile's project-type default.

TDD: 18 new tests across 4 files, one per helper. The around-advice tests build the capture/install/orig-fn flow against stub cmd-maps and verify state captured, hook installed, orig-fn invoked. The revert hook tests cover failure-and-modified (revert), success (leave alone), failure-but-unchanged (leave alone), nil prior (leave alone), nil state (no-op), and self-removal. The reset-cmds tests cover the all-three-maps clear, no-cached-entry no-op, and no-project user-error.

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