[2/4] buzz-sdk: share the agent definition text rules

[Maxwellimus]

Desktop refuses a definition whose name or prompt carries invisible or control
characters — text that consumes input bytes without a visible glyph defeats the
human review that shared definitions depend on. That check lived in the Tauri
crate, so any other publisher could put a definition on the relay that Desktop
then declines to launch: it publishes clean and fails later, which reads as a
Desktop bug.

Moves the rules to buzz_sdk::definition_validation and has Desktop delegate.

The SDK carries Extended_Pictographic as a literal range table rather than
pulling regex onto every binary's dependency path. Desktop already depends on
regex, so the exhaustive comparison against \p{Extended_Pictographic} runs
there — it walks the whole code space and fails if the table ever drifts from
the property, including when a future regex ships updated Unicode tables.

Test plan

• just ci
• cargo test --manifest-path desktop/src-tauri/Cargo.toml —
  sdk_pictographic_table_matches_the_unicode_property compares all 0x110000
  code points; currently byte-for-byte identical.

[wolfyy970]

Reviewed at exact head 063ae69b4c7b. This preserves the existing Desktop validation boundary while making it available to every definition publisher. The literal pictographic table matches Desktop’s Unicode property across the full scalar range, so CLI and Desktop cannot quietly diverge on emoji handling.

I reran the SDK and Desktop definition-validation suites, including that exhaustive comparison. All 11 focused tests passed; both Rust format checks and git diff --check are clean. The red Desktop check is an unrelated randomized passphrase test failure.

[wolfyy970]

Reviewed at exact head 358de84c55f3. I compared this to 063ae69b4c7b: the SDK and Desktop validation files are identical after the rebase onto current main. The earlier approval still applies.