fix(issue): Handle GitHub-style #SHORTID in issue identifiers

[sentry]

This PR addresses CLI-1G1, where sentry issue view commands were failing with a ValidationError: Invalid issue identifier: contains "#" (URL fragment).

Root Cause:
AI agents (like claude-code and codex) frequently pass GitHub-style issue identifiers such as org/project#SHORTID. The parseIssueArg function in src/lib/arg-parsing.ts was stripping / characters but not # before calling validateResourceId. The validateResourceId function, designed to prevent URL injection, correctly rejects # as a forbidden URL fragment character, leading to the ValidationError.

Solution:

1. Pre-process #fragment: In parseIssueArg, before the general validateResourceId call, a new parsing step detects and extracts a trailing #fragment.
2. Validate fragment: The extracted fragment (intended as the issue's short ID) is validated independently using validateResourceId to ensure it doesn't contain other forbidden characters.
3. Rewrite input: The original input is then rewritten to prefix/fragment (e.g., org/project/SHORTID) or just fragment if no prefix was present. This allows the existing slash-parsing logic to correctly interpret the identifier.
4. Improved error message: If the # is used incorrectly (e.g., multiple #s, empty fragment), a more helpful ValidationError is thrown, suggesting the correct org/project/SHORTID format.
5. Downstream flow: Subsequent parsing steps (numeric, colon, slash, dash, suffix-only) now operate on the normalized input, ensuring the rewritten value is processed correctly.

This change allows sentry issue view to correctly parse org/project#SHORTID inputs while maintaining robust validation against malicious or malformed identifiers.

Fixes CLI-1G1

[github-actions]

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