feat(0098): CLI clap migration (iteration 1) — scoped help, --version, GNU flags

Replace the hand-rolled aura-cli argv parser with a clap derive parser.
Delivers, all from one declarative source:
- scoped `aura <sub> --help` (stdout, exit 0) — each subcommand's own Options
  section; retires the #131 uniform-global-blob help
- `--version` / `-V` → `aura 0.1.0` (stdout, exit 0)
- GNU `--flag=value`, the `--` end-of-options terminator, and long-option
  abbreviation (`--harn` → `--harness`)

Architecture: one root Cli/Command enum, one `*Cmd` struct per subcommand. The
four dual-grammar subcommands (run/sweep/walkforward/mc) map the loaded-blueprint
branch as an optional `[blueprint]` positional + a post-parse `is_file()`
dispatch on a single-sourced predicate; each built-in handler re-asserts a
stray-positional guard (refuse-don't-guess) so clap's optional positional cannot
silently swallow a typo (pinned by two new E2E tests). The execution layer
(run_*/emit_*/runs_*/reproduce_*) is untouched — only arg-plumbing changes, via
thin `*_from` adapters reusing the existing value helpers.

Exit codes behaviour-preserved: clap parse errors exit 2 (matching the old
usage-error=2); domain refusals stay exit 2; reproduce-diverged stays exit 1.
The exit-code split (2=usage / 1=runtime) is iteration 2. clap is admitted under
the C16 per-case review (research-side CLI, invariant 8 untouched — a dev-loop
compile tax, not a frozen-artifact tax).

Forced plan corrections (implementer; verified against the diff):
- Step 6's deletion of the `parse_*_args` fns orphaned ~34 grammar unit tests
  that called them; those were deleted and that grammar coverage moved to the
  renegotiated cli_run.rs E2E pins (`parse_select` kept + retested).
- run_malformed_cost_value_...: a bad cost value is now a clap value-parse error
  (no "Usage:" line); renegotiated to pin exit 2 + empty stdout + the flag name
  "--cost-per-trade"; the units note stays pinned via `run --help`.
- `allow_hyphen_values` on the three cost flags so `--cost-per-trade -0.5`
  reaches the non-negativity guard (else clap rejects -0.5 as an unknown option).
- Deleted the now-dead `RealWindowGrammar` (clippy -D warnings).

Orchestrator additions after the loop:
- Enabled long-option abbreviation (`infer_long_args` on the root — one
  attribute, it propagates to subcommands) + a test, closing spec acceptance
  criterion 4 which the plan's RED tests did not cover. Decided to deliver
  rather than amend the spec: the two ratified decisions conflict on this
  low-tier item — Fork B (GNU compliance, getopt_long abbreviates) vs F5
  (LLM/automation-first, human-only niceties deprioritized) — and the cost
  tiebreaker (one attribute, not per-struct work) resolves to deliver.

Carry-on debt (not this iteration): the error-message "Usage:"/"usage:"/bare
casing is now mixed (clap's capitalized "Usage:" beside preserved lowercase aura
messages); a deliberate quality-hold since the casings are pinned by
renegotiated/preserved tests. Cosmetic; a candidate for the iteration-2
exit-code-split cleanup.

Verified green (orchestrator, this session): cargo build --workspace, cargo
clippy --workspace --all-targets -- -D warnings, and cargo test --workspace all
clean (0 failed across every test binary, including the renegotiated cli_run
pins and the new --version / scoped-help / GNU-flag / dual-grammar tests).

refs #175

crates/aura-cli/Cargo.toml

@@ -40,3 +40,9 @@ libc = "0.2"
 # SHA256 user-settled); lives in the research-side CLI, off the frozen engine
 # (invariant 8).
 sha2 = "0.10"
+# clap: the vetted standard argument parser. Adopted (C16 per-case review) to
+# replace the hand-rolled argv parser + ten duplicated help surfaces with one
+# declarative source, giving scoped --help, --version, --flag=value, and
+# long-option abbreviation. Research-side CLI only (invariant 8): a dev-loop
+# compile tax, never a frozen-artifact tax.
+clap = { version = "4", features = ["derive"] }