Rename Goal → Intent #2

No users, no existing session graphs. Do it now while the schema is free.

Changes in atomic:

• atomic-agent/src/provenance/types.rs — NodeKind::Goal → NodeKind::Intent, serialized as "intent"
• atomic-agent/src/provenance/accumulator.rs — rename all goal-prefixed fields and methods: current_goal → current_intent, append_goal() → append_intent(), GraphStats::goal_count → intent_count
• atomic-agent/src/provenance/classify.rs — update any classifier rules that reference Goal
• All existing graph.json test fixtures — update "kind": "goal" → "kind": "intent"
• Update atomic-cli output and any atomic log display strings

After this lands: atomic-tui can use NodeKind::Intent directly with no display-layer aliasing needed.