Add a composable ratatui TUI to ppvm-cli (#166)

## Summary

Adds a composable [ratatui](https://ratatui.rs) TUI to `ppvm-cli`. Bare
`ppvm` launches a unified single-screen REPL + step-debugger; `ppvm
<file>` opens a program paused at the first instruction. The existing
`run`/`dump`/`parse`/`debug` subcommands are unchanged.

- **New library crate `crates/ppvm-tui`** holds the terminal-agnostic
pieces: an `AppState` owning a `ppvm_vihaco::composite::PPVM`, the
command grammar, and four ratatui `Widget` view components
(Program/State/Measurement-record/Command line).
- **`ppvm-cli` (bin)** owns only terminal setup (RAII restore on panic)
and the blocking event loop.
- **Composability:** view components own no terminal and run no loop
(`impl Widget for &…View`-style; `handle_key(KeyEvent) -> bool`), and
deps are pinned to `ratatui`/`crossterm` `0.29.0` to match
`stellarscope` so panels can dock together later.

### Features
- **REPL:** `device N` then gate ops (`h 0`, `cnot 0 1`, `rx 0 0.5`,
`measure 0`, …); outcomes echo as `=> bits`.
- **Debugger:** `:load`, Enter = step, `:c` = continue to next
breakpoint/end, `:reset`; authored `breakpoint`s pause.
- **Breakpoint gate injection:** at a breakpoint you can apply ad-hoc
gates and resume — backed by making `apply_circuit_instruction` preserve
the program counter (`ppvm-vihaco`).
- **Line editing + history:** movable cursor (←/→, Home/End,
insert/Backspace/Delete) drawn via the terminal cursor; ↑/↓ command
history with a draft stash.
- **`:help`** toggles a command-reference overlay (works in both modes).

## Base branch

Targets **`david/42-circuit-component`** (not `main`) — this branch was
cut from it and depends on its `vihaco-circuit-isa` work. The merge
commit here also pulls in that branch's `Add back eyre` fix (a
pre-existing derive-macro build breakage), so the branch compiles.

## Design docs
- Spec: `docs/superpowers/specs/2026-07-01-cli-tui-design.md`
- Plan: `docs/superpowers/plans/2026-07-01-cli-tui.md`

## Testing
- `cargo test --workspace` — green (0 failures).
- `ppvm-tui`: 36 tests (command grammar, REPL/debug state transitions,
breakpoint injection resume, cursor/history editing, help toggle,
`TestBackend` render checks).
- `clippy --all-targets` clean.

Built TDD, task-by-task, with per-task + whole-branch review.

**Draft:** opened for review before it's ready to merge.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: 3 people

.github/workflows/ci.yml

@@ -70,11 +70,12 @@ jobs:
         run: cargo test -p ppvm-stim --features rayon
 
   # Cross-compile the whole workspace for browser wasm so a wasm regression
-  # surfaces in CI. `ppvm-python-native` (a CPython extension) and `ppvm-cli`
-  # (a terminal binary using clap and forcing the rayon feature) are never
-  # browser-wasm targets and are excluded; the reusable engine lives in the
-  # library crates, which stay covered. Native-only acceleration deps (gxhash,
-  # dashmap → rayon, ahash) are pruned automatically by the `cfg(not(target_arch =
+  # surfaces in CI. Three crates are never browser-wasm targets and are
+  # excluded: `ppvm-python-native` (a CPython extension), `ppvm-cli` (a terminal
+  # binary), and `ppvm-tui` (its ratatui/crossterm terminal UI). The reusable
+  # engine lives in the library crates, which stay covered. Native-only
+  # acceleration deps (gxhash, dashmap →
+  # rayon, ahash) are pruned automatically by the `cfg(not(target_arch =
   # "wasm32"))` dependency tables, and `rand`'s entropy uses the getrandom
   # `wasm_js` backend wired in `.cargo/config.toml` — so no extra flags here.
   wasm-build:
@@ -91,7 +92,7 @@ jobs:
       - uses: Swatinem/rust-cache@v2
 
       - name: Build workspace for wasm32-unknown-unknown
-        run: cargo build --target wasm32-unknown-unknown --workspace --exclude ppvm-python-native --exclude ppvm-cli
+        run: cargo build --target wasm32-unknown-unknown --workspace --exclude ppvm-python-native --exclude ppvm-cli --exclude ppvm-tui
 
   python-tests:
     name: Python tests