fix(events): skip unreadable extension manifests

[marcelsafin]

Description

The raw-manifest fallback in collect_extension_events() skips malformed YAML and undecodable text, but an OSError from reading the same optional extension.yml escapes and aborts event collection.

This handles read failures at the existing best-effort boundary, so one inaccessible extension manifest does not block events from the rest of the project.

Testing

• Tested locally with uv run specify --help
• Ran existing tests with uv sync && uv run pytest (6,652 passed, 177 skipped)
• Added an unreadable-manifest regression using a targeted Path.read_text failure
• uvx ruff@0.15.0 check src tests clean

AI Disclosure

• I did not use AI assistance for this contribution
• I did use AI assistance (describe below)

Implemented autonomously by GitHub Copilot CLI (model: GPT-5.6 Sol) under human direction; a failing regression was added before the fix, then the full suite and lint were run locally. Commit includes Assisted-by and Co-authored-by trailers.

[Copilot]

Pull request overview

Handles unreadable optional extension manifests without aborting event collection.

Changes:

• Catches OSError when reading raw manifests.
• Adds regression coverage for read failures.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/specify_cli/events.py	Skips manifests that cannot be read.
tests/integrations/test_events.py	Tests unreadable-manifest handling.

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