feat(config): expose FORGE_* env vars via :config-env command

[chengyixu]

Fixes #2638

Problem

Many Forge configuration knobs (retry limits, HTTP timeouts, tool timeouts, file size limits, tuning parameters) are only discoverable by reading source code. Changing them requires manually editing .forge.toml or setting environment variables — there is no in-shell way to list what is configurable or to set a value interactively.

Solution

This PR adds a :config-env (:ce) command and the corresponding CLI plumbing so users can browse, inspect, and set all FORGE_* environment variables without leaving the terminal.

CLI changes

Command	Behaviour
forge config get env	Lists all 40+ known FORGE_* vars with current values, defaults, and descriptions
forge config get env KEY	Shows the current value of a single variable
forge config set env KEY VALUE	Writes the value to ~/.forge/.forge.toml and applies immediately (no restart)

ZSH changes

• :config-env / :ce — opens an fzf picker populated by forge config get env; selecting a variable prompts for a new value and calls forge config set env automatically
• Registered in built_in_commands.json so it appears in :help and tab completion

Architecture

• env_registry module in forge_config — a static catalogue mapping each FORGE_* env var to its TOML key, default value, and description. This is the single source of truth for discoverability.
• Config persistence — values are written to the global ~/.forge/.forge.toml (not .env), consistent with the existing config system and ForgeConfig::write() path.
• Type-aware TOML serialization — values are parsed as bool, integer, float, or string before writing, so the TOML file stays well-typed.
• Immediate effect — the env var is also set in the running process via std::env::set_var so changes take effect without restarting.

Example

# List all configurable variables
$ forge config get env
ENVIRONMENT VARIABLES
  FORGE_TOOL_TIMEOUT_SECS   300  (default)  # Max seconds a tool call is allowed to run
  FORGE_MAX_SEARCH_LINES    1000  (default)  # Max lines returned by file search
  ...

# Get a specific variable
$ forge config get env FORGE_TOOL_TIMEOUT_SECS
FORGE_TOOL_TIMEOUT_SECS (not set, default: 300)

# Set a variable (writes to .forge.toml, applies immediately)
$ forge config set env FORGE_TOOL_TIMEOUT_SECS 60
● FORGE_TOOL_TIMEOUT_SECS  set to '60' in /home/user/forge/.forge.toml

# Or interactively via ZSH
:ce   # Opens fzf picker → select variable → enter value

Variables exposed

40+ FORGE_* variables covering: tool timeouts, file size limits, search limits, stdout truncation, HTTP/TLS config, retry settings, semantic search parameters, tuning parameters (temperature, top_p, top_k, max_tokens), and more.

Files changed

File	Change
crates/forge_config/src/env_registry.rs	New: static registry of all FORGE_* variables
crates/forge_config/src/lib.rs	Export new module
crates/forge_main/src/cli.rs	Add Env variants to ConfigSetField and ConfigGetField
crates/forge_main/src/ui.rs	Implement handle_config_env_set and handle_config_env_get handlers
crates/forge_main/src/built_in_commands.json	Register :config-env command
crates/forge_main/Cargo.toml	Add forge_config and toml_edit dependencies
shell-plugin/lib/dispatcher.zsh	Route :config-env / :ce to action handler
shell-plugin/lib/actions/config.zsh	New _forge_action_config_env function with fzf picker

Test plan

• All 245 forge_main library tests pass
• All 11 forge_config tests pass (including 4 new env_registry tests)
• All 75 CLI parsing tests pass
• Zero clippy warnings
• cargo check succeeds

Co-Authored-By: ForgeCode noreply@forgecode.dev

[CLAassistant]

All committers have signed the CLA.

[graphite-app]

Data Loss: Silent Parse Error Handling

If the existing .forge.toml contains invalid TOML syntax, unwrap_or_default() silently creates an empty document and overwrites the file, destroying all existing configuration.

Fix: Return the parse error instead of silently discarding it:

let mut doc: toml_edit::DocumentMut = existing.parse()
    .map_err(|e| anyhow::anyhow!("Failed to parse existing config file: {e}"))?;

Suggested change

	let mut doc: toml_edit::DocumentMut = existing.parse().unwrap_or_default();
	let mut doc: toml_edit::DocumentMut = existing.parse().map_err(|e| anyhow::anyhow!("Failed to parse existing config file: {e}"))?;

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[chengyixu]

recheck