feat(ask): add --inline-max-bytes per-run override

[sam-saffron-jarvis]

Adds term-llm ask --inline-max-bytes <size> to override ask.stdin_inline_max_bytes for a single run.

Why

Since 2cc3b291 (structured ask input attachments), text from stdin / -f larger than ask.stdin_inline_max_bytes (default 10 KiB = 10240 bytes) is staged as a file and the model must read_file it. Scripted single-turn runs with deliberately large prompts break: the Jarvis daily digest passes a ~166 KB prompt with --max-turns 1 and failed three days running with agentic loop exceeded max turns (1). The only fix was a global config change; this makes it per-invocation.

Behaviour

• Accepts plain bytes or human sizes via go-humanize: 4096, 512K (512,000), 2MiB (2,097,152).
• Must be positive and ≤ ask.stdin_max_bytes (default 20 MiB = 20,971,520); errors otherwise, e.g. 50MiB → must not exceed ask.stdin_max_bytes (20971520).
• Empty/unset leaves config untouched. stdin_max_bytes is never changed.
• github.com/dustin/go-humanize moves from indirect to direct (already in the module graph).

Verification

• New unit tests: parsing/validation table, and a ~168 KB text source that is staged under the 10 KiB default but inlined with 1MiB.
• go test ./cmd, go build ./..., go vet ./cmd, make complexity pass.
• Live: 180,030-byte file with a secret word at the end, --max-turns 1:
  • --inline-max-bytes 4K → agentic loop exceeded max turns (1)
  • --inline-max-bytes 1MiB → PERSIMMON
• Docs: configuration reference + usage guide.