docs(fork): rebased upstream heads of the Session volume series

[teemow]

Problem

The upstream pull requests of the Session volume series (kagent-dev#3155, kagent-dev#3156, kagent-dev#3157, kagent-dev#3158) conflict with upstream main, which moved 17 commits since their base: kagent-dev#3153 replaced the controller's application environment variables with a config schema, kagent-dev#3160 changed the PostgreSQL config, kagent-dev#3080 the Agent's template shape, kagent-dev#3185 the import grouping. The carried files still name only the old heads.

Proposed solution

Each carried file of the series names its rebased upstream head, prepared on the mirror main @ b42a6c53a and queued on the team's upstream review list (rows 207 and 208):

• api-workspace-volume-reference-and-admission-token: upstream/session-volume-source-3.
• session-configurable-admission-verifying-a-signed: upstream/session-admission-jwt-3, configured by the controller config's sessions.admission.jwt upstream; the line keeps its environment variables until the re-pin onto that main.
• harness-claude-in-its-session-directory-changed: upstream/claude-session-directory-2.
• adk-set-up-the-session-directory: upstream/adk-session-directory-2.
• harness-tell-a-returning-claude-session-its-directory-was-set-up-again: upstream/claude-fresh-directory-notice-2.

The open upstream pull requests are not touched; their owner moves them to the new heads.

Acceptance criteria

• scripts/fork/carried.sh --check passes (fork-ledger)
• Each carried file of the series names its rebased branch and review-list row