Allow editing and deleting individual time entries

[grmbyrn]

Problem

Once a time entry is saved there is no way to correct it. Any mistake
(wrong duration, wrong client) is permanent, making the tool unreliable
for real billing use.

Proposed Solution

Add edit and delete actions to each time entry in the timer/log view.

Acceptance Criteria

• Each time entry row has an Edit and Delete button
• Edit opens an inline form or modal to update start time, end time, and client
• Delete prompts a confirmation before removing the entry
• API routes PUT /api/timer/[id] and DELETE /api/timer/[id] are implemented with ownership checks

Labels

enhancement, high-priority