feat: version 4.4.0 -- Calendario de reuniones

Menu Calendario (Mes/Semana/Dia/Agenda) para agendar reuniones con participantes
internos y externos, RSVP, vinculo a proyecto, vencimientos de actividades,
invitaciones iCalendar por correo, recurrencia con excepciones, recordatorios
in-app y aviso de choques. Migracion 034_meetings.sql.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/database/migrations/034_meetings.sql

@@ -0,0 +1,65 @@
+SET NAMES utf8mb4;
+
+CREATE TABLE IF NOT EXISTS meetings (
+  id INT AUTO_INCREMENT PRIMARY KEY,
+  uid CHAR(36) NOT NULL UNIQUE,
+  title VARCHAR(160) NOT NULL,
+  description TEXT NULL,
+  starts_at DATETIME NOT NULL,
+  ends_at DATETIME NOT NULL,
+  all_day TINYINT(1) NOT NULL DEFAULT 0,
+  location VARCHAR(255) NULL,
+  video_url VARCHAR(2048) NULL,
+  project_id INT NULL,
+  organizer_id INT NOT NULL,
+  reminder_minutes SMALLINT UNSIGNED NULL,
+  recurrence_json TEXT NULL,
+  sequence_number INT UNSIGNED NOT NULL DEFAULT 0,
+  edit_version INT UNSIGNED NOT NULL DEFAULT 1,
+  cancelled_at DATETIME NULL,
+  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  INDEX idx_meetings_range (starts_at, ends_at, cancelled_at),
+  INDEX idx_meetings_project (project_id, starts_at),
+  INDEX idx_meetings_organizer (organizer_id, starts_at),
+  CONSTRAINT fk_meetings_project FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE SET NULL,
+  CONSTRAINT fk_meetings_organizer FOREIGN KEY (organizer_id) REFERENCES users(id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+CREATE TABLE IF NOT EXISTS meeting_participants (
+  meeting_id INT NOT NULL,
+  user_id INT NOT NULL,
+  rsvp ENUM('pending','accepted','declined','tentative') NOT NULL DEFAULT 'pending',
+  responded_at DATETIME NULL,
+  PRIMARY KEY (meeting_id, user_id),
+  INDEX idx_meeting_participants_user (user_id, meeting_id),
+  CONSTRAINT fk_mp_meeting FOREIGN KEY (meeting_id) REFERENCES meetings(id) ON DELETE CASCADE,
+  CONSTRAINT fk_mp_user FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+CREATE TABLE IF NOT EXISTS meeting_external_participants (
+  meeting_id INT NOT NULL,
+  email VARCHAR(160) NOT NULL,
+  PRIMARY KEY (meeting_id, email),
+  CONSTRAINT fk_mep_meeting FOREIGN KEY (meeting_id) REFERENCES meetings(id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+CREATE TABLE IF NOT EXISTS meeting_exceptions (
+  meeting_id INT NOT NULL,
+  occurrence_start DATETIME NOT NULL,
+  created_by INT NULL,
+  created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  PRIMARY KEY (meeting_id, occurrence_start),
+  CONSTRAINT fk_mex_meeting FOREIGN KEY (meeting_id) REFERENCES meetings(id) ON DELETE CASCADE,
+  CONSTRAINT fk_mex_user FOREIGN KEY (created_by) REFERENCES users(id) ON DELETE SET NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+CREATE TABLE IF NOT EXISTS meeting_reminders (
+  meeting_id INT NOT NULL,
+  occurrence_start DATETIME NOT NULL,
+  sent_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  PRIMARY KEY (meeting_id, occurrence_start),
+  CONSTRAINT fk_mr_meeting FOREIGN KEY (meeting_id) REFERENCES meetings(id) ON DELETE CASCADE
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+ALTER TABLE notifications MODIFY COLUMN entity_type ENUM('project','activity','meeting') NULL;