Refactor the design of bottombox of Chatbox UI

[Douglasymlai]

Closes #1729

Related Issue

New Feature

Description

Refactors the ChatBox BottomBox composer into a clearer two-tier layout and adds new picker / project-setup controls.

Layout & structure

• Introduces BoxBottom — a dedicated row under the input for project-setup controls (session mode, model, thinking effort), separate from the message composer in InputBox.
• Moves session mode and model dropdown out of InputBox and into BoxBottom; both render read-only once a project has started, interactive on the workspace composer.
• Removes BoxAction (task time, status, pause/resume) from the bottom bar.
• Restructures floating overlays (queued messages, usage-limit banner, picker panels) so they sit above BoxMain without affecting layout.
• Updates shell styling: rounded-3xl, revised background tokens, and a subtle backdrop on the chat overlay container.

New UI

• PickerPanel — floating connector and skill pickers triggered from the input action row; toggling inserts/removes #skill / @connector tokens inline.
• ThinkingEffortSelect — pill-style reasoning-effort control matching the model dropdown and mode toggle (UI only for now; fixed to Medium, not yet persisted per project — tracked in [Feature Request] Add model thinking effort controls #1717).
• ProjectModeToggle — read-only variant for in-project chat (transparent background, no chevrons).

Input & rich text

• Replaces the generic “+” menu with dedicated connector (hammer) and skill (wand) trigger buttons.
• Extends rich-text parsing/rendering to support @connector tokens alongside existing #skill tokens.
• Extracts shared integration logos into src/lib/connectorIcons.ts (reused by the picker and Connectors settings page).

Other

• Tweaks ChatInputModelDropdown trigger styling (removes Sparkles icon, grows to menu width while open).
• Adds i18n strings for thinking-effort labels and add-connector/skill actions across all locales.

Testing Evidence (REQUIRED)

• I have included human-verified testing evidence in this PR.
• This PR includes frontend/UI changes, and I attached screenshot(s) or screen recording(s).
• No frontend/UI changes in this PR.

Manual verification:

• Workspace empty state — BottomBox shows interactive mode toggle, model dropdown, and thinking-effort control on the bottom row.
• Active project chat — bottom row renders read-only; input action row shows connector/skill triggers and send button.
• Connector picker — opens above input, toggles @connector tokens, closes on outside click.
• Skill picker — opens above input, toggles #skill tokens, closes on outside click.
• Long model names — bottom row wraps instead of clipping (regression for [BUG] Chat input bottom row overflows / clips instead of folding when content doesn't fit #1729).
• Queued messages and usage-limit banner still float above the composer without shifting layout.
• Confirm/save states — header variants and background colors render correctly.

Note: Attach screenshots or a screen recording showing the workspace composer, in-project read-only bottom row, and connector/skill picker panels before requesting review.

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Contribution Guidelines Acknowledgement

• I have read and agree to the Eigent Contribution Guideline

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