docs: update ROADMAP, SPRINTS, and BUGS to v0.50.156 — 1903 tests

Update sprint history table in ROADMAP.md through v0.50.156, fix test count header, add Known Limitations section to BUGS.md, update SPRINTS.md header. Reviewed by Opus — factually accurate, table column alignment fixed.

BUGS.md

@@ -10,6 +10,18 @@ This file tracks UI bugs and polish items. Fixed items are kept for reference.
 
 ---
 
+## Known Limitations
+
+- **Two-container Docker setup: tools run in WebUI container** — In the two-container setup (hermes-agent + hermes-webui as separate containers), WebUI-initiated agent sessions run tools in the WebUI container, not the agent container. This is a known architectural constraint. Workaround: use the combined single-image approach, or initiate sessions via the CLI in the agent container. (#681)
+
+- **Image-in-chat vs. saved-to-workspace mismatch** — When the agent displays an inline image (from a URL) and the user asks it to save that image, the agent issues a fresh download which may return a different file if the source URL is CDN-rotated or parameterized. The WebUI correctly renders whatever URL the agent provides. Fix requires agent-side URL caching. (#641)
+
+- **MCP tools not available in WebUI sessions** — MCP servers must be configured in the active profile's config.yaml under mcp_servers:. If MCP tools are not appearing, check that the profile is correct and the MCP server process is reachable from inside the WebUI container. (#628)
+
+- **os.environ race condition in concurrent sessions** — Concurrent agent sessions share process-level os.environ for TERMINAL_CWD, HERMES_SESSION_KEY, and HERMES_HOME. _ENV_LOCK serializes mutations but does not fully isolate env vars during agent execution. Upstream fix pending in hermes-agent. (#195)
+
+---
+
 ## Fixed
 
 ### ~~Session title truncation / hover actions~~ -- Fixed (Sprint 16)