docs: fix GH_AW_AGENT_TOKEN fallback behavior documentation

[Copilot]

The GH_AW_AGENT_TOKEN section contained contradictory statements about token fallback behavior. One part claimed "no further fallback", while another described fallback to GH_AW_GITHUB_TOKEN/GITHUB_TOKEN. The implementation uses GH_AW_AGENT_TOKEN || GH_AW_GITHUB_TOKEN || GITHUB_TOKEN (see pkg/workflow/github_token.go:getEffectiveAgentGitHubToken).

Changes

• Added explicit "Token precedence and fallback" section documenting the fallback chain
• Removed contradictory "no further fallback" statement
• Simplified redundant token precedence text in Technical Implementation note to reference main section

The documentation now accurately reflects the runtime behavior:

# Token resolution order:
# 1. GH_AW_AGENT_TOKEN (if set)
# 2. GH_AW_GITHUB_TOKEN (fallback)
# 3. GITHUB_TOKEN (final fallback)

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[Copilot]

Pull request overview

Updates the token reference docs to remove contradictory statements about GH_AW_AGENT_TOKEN fallback behavior and align the documentation with the actual runtime token resolution logic used by gh-aw.

Changes:

• Added an explicit “Token precedence and fallback” section under GH_AW_AGENT_TOKEN and removed the prior “no further fallback” claim.
• Simplified the “Technical Implementation” note to reference the main precedence/fallback section instead of repeating details.
• Updated the pinned commit for docker/build-push-action in the release workflow lockfile and added a corresponding entry to the actions lock JSON.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
docs/src/content/docs/reference/tokens.md	Clarifies GH_AW_AGENT_TOKEN fallback behavior and removes contradictory wording.
.github/workflows/release.lock.yml	Updates the pinned SHA for docker/build-push-action used by the release workflow.
.github/aw/actions-lock.json	Adds a lock entry for docker/build-push-action@v6 to match the updated pin.

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[Copilot]

The new bullets describe GH_AW_AGENT_TOKEN as "always used" when set, but runtime precedence in getEffectiveAgentGitHubToken uses a custom/per-output token and top-level github-token before checking GH_AW_AGENT_TOKEN. This section should reflect the full precedence (custom/per-output → workflow-level → GH_AW_AGENT_TOKEN → GH_AW_GITHUB_TOKEN → GITHUB_TOKEN) or reword to avoid implying env var wins over explicitly configured tokens.

Suggested change

	- If `GH_AW_AGENT_TOKEN` is set, it is always used for agent assignment.
	- If `GH_AW_AGENT_TOKEN` is _not_ set, `gh-aw` falls back to `GH_AW_GITHUB_TOKEN`, and then to `GITHUB_TOKEN`, matching the runtime resolution `GH_AW_AGENT_TOKEN || GH_AW_GITHUB_TOKEN || GITHUB_TOKEN`.
	- For agent assignment, `gh-aw` first uses any token explicitly configured for the safe output (for example, a custom/per-output token), then any workflow-level `github-token` input.
	- If neither of those is provided and `GH_AW_AGENT_TOKEN` is set, it is used next for agent assignment.
	- If `GH_AW_AGENT_TOKEN` is _not_ set, `gh-aw` falls back to `GH_AW_GITHUB_TOKEN`, and then to `GITHUB_TOKEN`, matching the runtime resolution: custom/per-output → workflow-level → `GH_AW_AGENT_TOKEN` → `GH_AW_GITHUB_TOKEN` → `GITHUB_TOKEN`.

[Copilot]

This PR is described as a documentation-only fix, but this change also updates the pinned docker/build-push-action commit in the release workflow lockfile. Please either mention this action bump in the PR description (so reviewers understand the extra change) or split it into a separate PR to keep the docs change focused.