Add escalate: push a new needs_human blocker to Telegram

[lorenzoliuzzo]

Summary

fleet-dispatch#44, part of fleet-dispatch#46 Phase 2 (Decide).

• `mydirector escalate --dispatch-ledger --bot-ledger` reads fleet_dispatch's own dispatch ledger straight off disk for `needs_human` entries — the same read-only seam `sources.py` already uses to surface MyPlanner's latest sequence — and shells out to `mytelegrambot escalate-blocker` (companion PR Push needs_human blockers to Telegram with Retry/Skip/take buttons my-telegram-bot#36) for each new one.
• Each candidate is escalated at most once (dedup via a `kind=escalated` ledger entry); a failed push is deliberately not recorded, so it's retried next run instead of silently lost — same posture as `notify()`/`send_spend_alert()`.
• `_bot_binary()` resolution mirrors `fleet_ask.py`'s: prefer the console script beside the running interpreter, fall back to `PATH`.

Test plan

• `python -m pytest -q` — 37/37 pass
• `--cov=mydirector` — `escalate.py` at 96% (the two uncovered lines are a defensive OSError/ValueError catch identical in shape to `sources.py`'s own, never actually raised by `Ledger`), 93% overall, clears the repo's `fail_under=85` gate
• `ruff check .` clean

Refs MyThingsLab/fleet-dispatch#44, MyThingsLab/fleet-dispatch#46

[codecov]

Codecov Report

❌ Patch coverage is 97.33333% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/mydirector/escalate.py	96.29%	2 Missing ⚠️

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