refactor(plugins): pin anthropic to 1.48, drop redundant colon check, trim docs

[kiro-agent]

This pull request was created by @kiro-agent on behalf of @galuszkm 👻

Comment with /kiro fix to address specific feedback or /kiro all to address everything.
_{Learn about Kiro Web}

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Follow-up review fixups for #75, targeting the PR branch so it merges straight in.

Changes

• Dependency parity — pin the anthropic extra to strands-agents>=1.48.0 (was left at 1.35.0 while base + ollama/openai/gemini moved to 1.48.0), in pyproject.toml and uv.lock.
• Thinner resolvers — drop the redundant ':' not in type check from resolve_plugin and resolve_hook. load_object already raises ImportResolutionError (a ValueError subclass) on a malformed spec, so behaviour and the existing tests (which match on "import spec") are unchanged; docstrings updated accordingly.
• Docs — trim Chapter 19's duplicated SKILL.md authoring deep-dive down to a pointer at the strands / Agent Skills docs (that content is owned by strands, not strands-compose); lighten the params path note and flag it may change in a future release; update the error table (missing : now flows through load_object).
• Typo — fix the project-map.md stack-note (gemini. anthropic. → gemini, anthropic).

Testing

• uv run just check — clean (ruff format + lint, ty, bandit).
• uv run just test — 232 passed, 76.46% coverage.

Note: opened as a delta against feat/mg/plugins because the sandbox gateway could not fast-forward the PR branch directly. Merging this into feat/mg/plugins updates #75.

[galuszkm]

lgtm