feat: Add persistent chat history with directory isolation

[jmmoser]

Issue #, if available:
#2633

Same as #2635, just a different branch from head repository.

Description of changes:

Implements persistent chat history that survives CLI restarts and is isolated by working directory.

Features:

• Chat history persists across CLI sessions using SQLite database
• History is isolated per working directory (/project/a vs /project/b)
• Up arrow navigation works with persistent history
• Dual cleanup limits: max 100 entries per directory, 1000 total
• Silent failure: history issues don't break CLI functionality
• Filters out empty/whitespace-only and confirmation inputs

Implementation:

• Database table: chat_readline_history(input TEXT, cwd TEXT, timestamp INTEGER) with index on cwd and timestamp
• Uses existing database infrastructure and Os abstraction
• Transactional insert+cleanup for data consistency
• Early return for empty inputs to avoid unnecessary DB operations

Files modified:

• crates/chat-cli/src/database/mod.rs: Added add_chat_readline_history_entry() and get_chat_readline_history()
• crates/chat-cli/src/cli/chat/input_source.rs: Load history on startup, save on input

Edge cases handled:

• Database failures (silent)
• Empty/whitespace and confirmation inputs (filtered)
• Working directory access failures (fallback to default)
• Unicode/special characters (parameterized queries)

Interaction with other features:

• Does not conflict with --resume. It enhances it.
• Does not conflict with /load.

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