feat(local-model): hardware probe, model catalogue and the pure recommendation

The core of the read-only recommendation: what this Mac is, what the catalogue
knows, and which model fits. Nothing is downloaded, installed or written.

- hardware.ts: one bounded async spawn of /usr/sbin/sysctl with seven keys,
  without -n, parsed as "key: value" lines by the pure parseSysctl(). Free disk
  of the data dir through statfs behind the bounded path probe. Fallbacks from
  node:os, a 60 s cache, never throws, never system_profiler. A wired limit of
  0 means "not set".
- local-model-catalog.ts: seven models, three harness rows (pi gated) and the
  chips table as a compiled constant, validated by a Zod schema on first use.
  No override file. Model ids are name:tag in lowercase without a slash; every
  model carries paramsB and an (empty) tested list. Chip names match on the
  end of the chip string, so 'M4' is not the chip of 'Apple M4 Pro'.
- recommend.ts: device budget (the wired limit when above 0, else 2/3 of
  memory below 36 GB and 3/4 from 36 GB, less the reserve), need = weights +
  KV cache + 1 GiB + prompt cache, fit good up to 0.85 and tight up to 0.98,
  speed ok, unknown or slow (a chip in no chips row is unknown), and the
  ranking. Verdicts ok, limited (best model under 12 billion parameters) and
  none with its reason. "Recommended" only for a pick with a tested entry for
  this Mac, which no row has today.
- types/local-model.ts: comments brought in line with the code (chip matching,
  budgetShare rounding, a budget of 0 on an Intel Mac).
- cli-registry-no-id-branching.test.ts: the guard also catches a comparison of
  a `cli` field with a CLI id (plus one stray blank line Prettier refused).

Tests: test/local-model-format.test.ts, test/local-model-hardware.test.ts
(the captured output of two real Macs), test/local-model-catalog.test.ts,
test/local-model-recommend.test.ts.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/types/local-model.ts

@@ -129,11 +129,14 @@ export interface LocalHarnessEntry {
 
 /**
  * Memory bandwidth of one chip family. `LocalModelCatalog.chips` is ordered most specific first
- * ('M4 Max' before 'M4') and the first row whose `match` occurs in `HardwareFacts.chip` wins. A
- * chip that matches no row has an UNKNOWN speed: a bandwidth is never guessed.
+ * ('M4 Max' before 'M4') and the first row that names `HardwareFacts.chip` wins. A row names a
+ * chip when the chip string ENDS with its `match`, starting at the beginning or after a space,
+ * case ignored (`chipNameMatches()` in src/config/local-model-catalog.ts): 'M4' is not the chip
+ * of 'Apple M4 Pro', and a variant the table has never heard of ('Apple M6 Pro') matches no row.
+ * A chip that matches no row has an UNKNOWN speed: a bandwidth is never guessed.
  */
 export interface ChipEntry {
-  /** Text that must occur in the chip string ('M4 Max'). */
+  /** The chip name the chip string must end with ('M4 Max'). */
   match: string;
   /** Memory bandwidth in GB/s. */
   gbps: number;
@@ -305,7 +308,7 @@ export interface Candidate {
   downloadBytes: number;
   /** `downloadBytes` as decimal GB text, no unit. */
   downloadGb: string;
-  /** `needBytes / Recommendation.budgetBytes` (0.83). */
+  /** `needBytes / Recommendation.budgetBytes`, rounded to three decimals (0.83). The fit grade is decided on the unrounded ratio. */
   budgetShare: number;
   /** A candidate in a `Recommendation` is never `out`. */
   fit: Exclude<FitGrade, 'out'>;
@@ -339,7 +342,7 @@ export interface Recommendation {
   pick?: Candidate;
   /** The next models that fit (at most four, each at its best context and harness), best first. Empty when `verdict` is `none`. */
   alternatives: Candidate[];
-  /** `DeviceBudget.budgetBytes`. 0 when the budget could not be computed (not macOS). */
+  /** `DeviceBudget.budgetBytes`. 0 when no budget is computed: not macOS, or a Mac without Apple silicon. */
   budgetBytes: number;
   /** `budgetBytes` as decimal GB text, no unit. */
   budgetGb: string;