refactor: Clean up Cargo dependencies - remove unused, update outdated

- Remove unused const_format from g3-planner (never imported)
- Remove unused thiserror from workspace and 5 crates (declared but never used)
- Update termimad 0.31 -> 0.34 in studio (consistency with g3-cli)
- Update indicatif 0.17 -> 0.18 in g3-cli
- Update ratatui 0.29 -> 0.30 in g3-cli
- Update walkdir 2.4 -> 2.5 in g3-core
- Update image 0.24 -> 0.25 in g3-computer-control (macOS + Linux)
- Update config 0.14 -> 0.15 in workspace

Blocked: reqwest 0.11 -> 0.12/0.13 requires breaking API changes to
bytes_stream() used in 4 providers - needs separate migration effort.

All tests pass. No behavior changes.

Agent: fowler

crates/g3-cli/Cargo.toml

@@ -23,10 +23,10 @@ dirs = "5.0"
 tokio-util = "0.7"
 sha2 = "0.10"
 hex = "0.4"
-indicatif = "0.17"
+indicatif = "0.18"
 chrono = { version = "0.4", features = ["serde"] }
 crossterm = "0.29.0"
-ratatui = "0.29"
+ratatui = "0.30"
 termimad = "0.34.0"
 regex = "1.10"
 syntect = "5.3"