fix(create-pr): Split compound shell command into parseable steps

[JoshFerge]

The create-pr skill's Step 1 used BASE=$(gh repo view ...) — a compound
shell expression that Claude Code cannot parse for permission matching. This
means users always get a permission prompt and cannot add an "always allow"
entry for it.

Splitting it into a standalone gh repo view command lets Claude Code see
each command individually. Claude can then match it against a simple
Bash(gh repo view*) allow pattern in settings.json, and future UX
improvements could offer "always allow" at the prompt itself.

Subsequent git commands now receive the branch name as a literal substitution
(e.g. git log main..HEAD) rather than a shell variable, keeping them clean
and allowable too.

[JoshFerge]

confirmed this worked during the making of this PR :D

[sentry]

Bug: The create-pr skill uses the literal string "BASE" in git commands, expecting an AI to substitute it. This will fail at runtime as "BASE" is not a valid git revision.
_{Severity: CRITICAL}

Suggested Fix

Revert to using standard bash variable substitution. Define the base branch using a command like BASE=$(gh repo view --json defaultBranchRef --jq .defaultBranchRef.name) and then use the $BASE variable in subsequent git commands to ensure a valid branch name is used.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: plugins/sentry-skills/skills/create-pr/SKILL.md#L34-L35

Potential issue: The `create-pr/SKILL.md` file was updated to use the literal string
`"BASE"` as a placeholder in `git log BASE..HEAD` and `git diff BASE...HEAD` commands.
The skill's instructions direct an AI agent to substitute this placeholder with a branch
name derived from a previous command. However, this substitution mechanism is not
supported. As a result, the `git` commands will be executed literally, causing them to
fail at runtime with a `fatal: ambiguous argument 'BASE': unknown revision` error. This
breaks the `create-pr` skill.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[JoshFerge]

it's an AI so it will know to substitute BASE for what we ran above