[Feature] Edit Quest backend logic

[karastoyanov]

✨ Feature Description

Allow admins to edit an existing coding quest via a PUT /api/quests/<quest_id> endpoint. All mutable fields can be updated while immutable metadata (id, created_at, quest_author) is preserved.

🧩 Problem Statement

There is currently no way to update a quest once it has been created. Admins need the ability to fix errors in quest content, adjust difficulty, or update test inputs/outputs without having to delete and recreate the quest.

💡 Proposed Solution

Add a PUT /api/quests/<quest_id> endpoint accessible only by the admins. The route validates the payload and persists the changes. Only fields present in the request body are updated (partial update support).

Mutable Fields

language          = db.Column(db.String(50),  nullable=False)
difficulty        = db.Column(db.String(50),  nullable=False)
quest_name        = db.Column(db.String(255), nullable=False)
condition         = db.Column(db.Text,        nullable=False)
function_template = db.Column(db.Text,        nullable=False)

# Inputs (input_0 is the null/edge-case test)
input_0  … input_9  = db.Column(db.Text, nullable=True)

# Outputs (output_0 is the null/edge-case test)
output_0 … output_9 = db.Column(db.Text, nullable=True)

example_solution  = db.Column(db.Text, nullable=True)

Immutable Fields

id           # Primary key — never editable
created_at   # Set on creation — never editable
quest_author # Original quest author — never editable

Error Responses

Status	Scenario
400	Validation failure — missing/invalid required field
403	Requester is not an admin
404	No quest found for the given quest_id

🔄 Alternatives Considered

• A PUT /api/quests/<quest_id> endpoint exists and is accessible only to admins
• All mutable fields can be updated via the endpoint
• id, created_at, and quest_author are immutable and cannot be modified
• updated_at is automatically refreshed on every successful edit
• Request body is validated — missing required fields return 400 Bad Request with descriptive errors
• Attempting to edit a non-existent quest returns 404 Not Found
• Unauthorized edit attempts return 403 Forbidden
• Unit tests cover: successful edit, partial update, missing required fields, unauthorized access, and quest not found

📋 Acceptance Criteria

• Criterion 1
• Criterion 2
• Criterion 3

🔗 Related Issues / Links

📎 Additional Context

• solved_times is intentionally excluded from the edit endpoint — it is managed by the quest-solve flow, not manual edits.