refactor(workspace): generalize worktree session-attribution schema

Replace the vendor-specific kimaki_*/opencode_* field names in the
worktree origin_session envelope with a runtime-agnostic shape:

    {
        "primary_id": "<opaque or null>",
        "ids": {
            "<runtime-id>": { "<subkey>": "<opaque or null>", ... }
        }
    }

DMC no longer enumerates runtime IDs or env-var names. The integration
layer registers what to capture via the new filter
'datamachine_code_worktree_runtime_signatures', mirroring the pattern
established by CliChannelTransport (v0.44.0).

Changes:
- inc/Abilities/WorkspaceAbilities.php: replace branded schema properties
  with primary_id + ids (free-form additionalProperties map).
- inc/Workspace/WorktreeContextInjector.php:
  * Document the filter contract and envelope shape in the file header.
  * resolve_origin_session() iterates registered runtimes generically and
    drops non-URL values for *_url subkeys.
  * summarize_session() normalizes ids, supports an explicit primary_id
    on stored envelopes, and falls back to runtime-precedence scanning.
  * migrate_legacy_origin_session() transparently projects pre-#416
    branded top-level keys (<runtime>_<subkey>) into the new envelope on
    read. The helper is isolated, structural (prefix/suffix split — no
    enumerated allowlist), and gated for future deletion via the
    documented 'datamachine_code_worktree_attribution_legacy_migrated_v2'
    option.
- inc/Environment.php: drop the enumerated brand list from the file
  header docblock per RULES.md layer-purity prose guidance.

Refs #416

Author: chubes4

inc/Abilities/WorkspaceAbilities.php

@@ -1544,14 +1544,17 @@ private function registerAbilities(): void {
 										),
 										'session'         => array(
 											'type'        => 'object',
-											'description' => 'Captured session identifiers (kimaki/opencode). Fields default to null when the corresponding env was not present at worktree creation.',
+											'description' => 'Captured session identifiers in a runtime-agnostic envelope. `primary_id` is the single renderer-friendly identifier downstream surfaces display. `ids` is a free-form map keyed by runtime ID (a string the integration layer chooses, e.g. via the `datamachine_code_worktree_runtime_signatures` filter); each entry is a string-map of subkeys (e.g. session_id, thread_id, thread_url, run_id) the integration chose to capture. DMC enumerates no runtime IDs and no subkeys.',
 											'properties'  => array(
-												'primary_id'         => array( 'type' => array( 'string', 'null' ) ),
-												'kimaki_session_id'  => array( 'type' => array( 'string', 'null' ) ),
-												'kimaki_thread_id'   => array( 'type' => array( 'string', 'null' ) ),
-												'kimaki_thread_url'  => array( 'type' => array( 'string', 'null' ) ),
-												'opencode_session_id' => array( 'type' => array( 'string', 'null' ) ),
-												'opencode_run_id'    => array( 'type' => array( 'string', 'null' ) ),
+												'primary_id' => array( 'type' => array( 'string', 'null' ) ),
+												'ids'        => array(
+													'type'                 => 'object',
+													'description'          => 'Map of runtime-id => { subkey => string|null }. Keys are opaque; DMC does not validate against a closed set.',
+													'additionalProperties' => array(
+														'type'                 => 'object',
+														'additionalProperties' => array( 'type' => array( 'string', 'null' ) ),
+													),
+												),
 											),
 										),
 										'task'            => array(

inc/Environment.php

@@ -4,10 +4,10 @@
  *
  * Public signal that a co-located coding agent runtime exists on this host.
  *
- * Data Machine Code is the bridge between WordPress and an external coding
- * agent runtime (Claude Code, OpenCode, kimaki, etc.). Its mere activation
- * is the declarative answer to "is there a coding agent here?" — there is
- * no separate marker file or constant to declare.
+ * Data Machine Code is the bridge between WordPress and an external
+ * coding-agent runtime. Its mere activation is the declarative answer to
+ * "is there a coding agent here?" — there is no separate marker file or
+ * constant to declare.
  *
  * Other plugins that ship disk-side artifacts for a coding agent (e.g.
  * Intelligence's SKILL.md sync, MEMORY.md disk writes, MCP bridges) should