fix(ui): keep prompt attachments in sync

[codenomadbot]

Fixes prompt-token/attachment desync for placeholder-backed attachments.

• Chip “×” removal now goes through PromptInputApi.removeAttachment() so the exact [Image #N] / [pasted #N] token is removed from the prompt at the same time.
• Placeholder cleanup is regex-based (tolerates whitespace/case) and avoids global whitespace-collapsing across the whole prompt.
• Paste-time indexing now derives from the current prompt text (scan highest counter in prompt) so counters don’t drift.
• Adds a small reconciliation effect: if a placeholder token is removed from the prompt by editing, the corresponding placeholder-backed attachment is removed from the bar/store.

Files:

• packages/ui/src/components/prompt-input/usePromptAttachments.ts
• packages/ui/src/components/prompt-input/attachmentPlaceholders.ts
• packages/ui/src/components/prompt-input/types.ts
• packages/ui/src/components/prompt-input.tsx
• packages/ui/src/components/session/session-view.tsx

Notes:

• Local npm run typecheck currently fails in this repo due to pre-existing packages/ui/src/stores/preferences.tsx errors (unrelated to this change).

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Yours, CodeNomadBot