Branch name validation rejects '#' character, breaking Azure DevOps integration

**Describe the bug**
The Claude Code Action rejects branch names containing the # character, which is required by the standard [Azure DevOps ↔ GitHub integration](https://learn.microsoft.com/en-us/azure/devops/cross-service/github-integration?view=azure-devops) for ticket linking. This makes Claude Code Action incompatible with a standard, widely-used enterprise workflow.

**Error**
`Action failed with error: Invalid branch name: "feature/AB#1992-sentry-enhancements".
Branch names must start with an alphanumeric character and contain only alphanumeric
characters, forward slashes, hyphens, underscores, or periods.`

**Root Cause**
The validation logic inside claude-code-action is more restrictive than GitHub's own API, which **does** accept # in branch names. The error is generated client-side before any request reaches GitHub.

**Context**
The Azure DevOps + GitHub integration uses `AB#` in branch names and PR titles to link work items across systems. This format is **not configurable** — it is the documented, idiomatic standard for that integration. Teams using both platforms have no alternative.

**Impact**
Teams using Claude Code Action alongside Azure DevOps are forced into one of three unacceptable options:

1. **Run gh CLI manually** — requires provisioning allowed bash commands, introducing security surface area
2. **Break Azure DevOps ticket linking** — defeats the purpose of the integration
3. **Migrate to a different code review tool** — significant team disruption

**Expected behavior**
Branch name validation should match GitHub's actual API rules, or be removed entirely in favor of letting GitHub's API surface errors if a name is truly invalid.

**Steps to Reproduce**

1. Set up the standard [Azure DevOps ↔ GitHub integration](https://learn.microsoft.com/en-us/azure/devops/cross-service/github-integration?view=azure-devops)
2. Create a branch following the required naming convention, e.g. feature/AB#1992-description
3. Trigger Claude Code Action on a PR from that branch
4. Observe validation failure

**API Provider**

[X] Anthropic First-Party API (default)
[ ] AWS Bedrock
[ ] GCP Vertex

**Proposed Fix**
Relax or remove the client-side branch name regex to allow #, aligning validation with GitHub's actual API constraints.

Start by locating the client-side branch-name validation in the TypeScript action and reproduce it with `feature/AB#1992-description`. Compare the accepted characters with the issue’s GitHub API requirement, then verify that a branch containing `#` proceeds without this validation error and that existing invalid-name behavior remains covered.

Written by the indexing model from the issue text.