Lint: align advisory flake8 with black (99), clear the E501/F84x backlog — closes #318 - #319

Closes #318.

What this does

1. Aligns the advisory flake8 pass with the project's own black config (line-length 99).

The advisory run used --max-line-length=88 while black --check . (blocking) enforces 99 — so every black-formatted line of length 89–99 was a permanent finding. Advisory findings on main: 1,184. After alignment alone: 195.

Config is now codified in a checked-in .flake8 (flake8 does not read pyproject.toml, so the [tool.flake8] section there was dead — and had it been read, it would have ignored E501 entirely):

• max-line-length = 99 (matches [tool.black])
• extend-ignore = E203, W503 — black-style conflicts
• extend-ignore = F401, F403, F405 — the deliberate star-import re-export pattern (main.py/runner.py re-export runtime/tools; every tool module resolves names through it) — hundreds of hits, zero signal
• per-file-ignores: telegram_mcp/runtime.py: E402 — imports there follow env/lock setup on purpose

The advisory CI step now just runs flake8 . --count --exit-zero --statistics and reads .flake8.

2. Clears the remaining non-complexity backlog (94 E501, 11 F841, 6 F811, 6 F541):

• long docstrings/comments and over-long string literals wrapped — string content unchanged (implicit concatenation)
• dead local bindings removed (result = await ... where the result was never read)
• shadowed duplicate test definitions in tests/test_runner.py removed (the newer duplicate of each shadowed test is the one that actually ran — the dead earlier definitions are deleted)
• f-prefix dropped from f-strings without placeholders

Result

The 56 remaining C901 hotspots are left visible on purpose — they are a refactoring backlog (worst: message_to_dict at 45, validate_id at 29), not something to churn in a lint PR. From here the advisory count is small enough to keep honestly near zero.

Verification

flake8 . --count --exit-zero --statistics   # 56, all C901
black --check .                             # clean
pytest -q                                   # 1221 passed

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